Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
  Case Tag  
Price  
Sales  
Tax %  
Raw Total  
Incl. Sales Tax  
Rounded  
to Penny  
Rounded  
to Nickel  
Rounded  
to Dime  
  Purchase #1 $118.70   11.462%   $132.3054   $132.31   $132.30   $132.30  
  Purchase #2 $193.50   11.804%   $216.3407   $216.34   $216.35   $216.30  
  Purchase #3 $111.49   11.625%   $124.4507   $124.45   $124.45   $124.50  
  Purchase #4 $195.43   6.461%   $208.0567   $208.06   $208.05   $208.10  
  Purchase #5 $250.28   13.436%   $283.9076   $283.91   $283.90   $283.90  
  Purchase #6 $211.37   3.850%   $219.5077   $219.51   $219.50   $219.50  
  Purchase #7 $151.27   7.758%   $163.0055   $163.01   $163.00   $163.00  
  7 purchase totals = $1,232.04       $1,347.5743   $1,347.59   $1,347.55   $1,347.60