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 $133.32   7.517%   $143.3417   $143.34   $143.35   $143.30  
  Purchase #2 $199.88   6.679%   $213.23   $213.23   $213.25   $213.20  
  Purchase #3 $186.53   8.720%   $202.7954   $202.80   $202.80   $202.80  
  Purchase #4 $150.80   6.180%   $160.1194   $160.12   $160.10   $160.10  
  Purchase #5 $146.51   3.808%   $152.0891   $152.09   $152.10   $152.10  
  Purchase #6 $29.59   6.193%   $31.4225   $31.42   $31.40   $31.40  
  Purchase #7 $183.28   7.638%   $197.2789   $197.28   $197.30   $197.30  
  7 purchase totals = $1,029.91       $1,100.2770   $1,100.28   $1,100.30   $1,100.20