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 $210.69   7.782%   $227.0859   $227.09   $227.10   $227.10  
  Purchase #2 $69.43   7.483%   $74.6254   $74.63   $74.65   $74.60  
  Purchase #3 $89.80   7.377%   $96.4245   $96.42   $96.40   $96.40  
  Purchase #4 $36.52   3.302%   $37.7259   $37.73   $37.75   $37.70  
  Purchase #5 $234.91   12.661%   $264.652   $264.65   $264.65   $264.70  
  Purchase #6 $24.30   13.516%   $27.5844   $27.58   $27.60   $27.60  
  Purchase #7 $182.54   4.535%   $190.8182   $190.82   $190.80   $190.80  
  7 purchase totals = $848.19       $918.9163   $918.92   $918.95   $918.90