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 $216.80   11.122%   $240.9125   $240.91   $240.90   $240.90  
  Purchase #2 $177.91   13.242%   $201.4688   $201.47   $201.45   $201.50  
  Purchase #3 $53.51   3.367%   $55.3117   $55.31   $55.30   $55.30  
  Purchase #4 $197.66   5.641%   $208.81   $208.81   $208.80   $208.80  
  Purchase #5 $42.55   5.869%   $45.0473   $45.05   $45.05   $45.00  
  Purchase #6 $228.60   11.521%   $254.937   $254.94   $254.95   $254.90  
  Purchase #7 $5.86   9.731%   $6.4302   $6.43   $6.45   $6.40  
  7 purchase totals = $922.89       $1,012.9175   $1,012.92   $1,012.90   $1,012.80