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 $226.42   11.572%   $252.6213   $252.62   $252.60   $252.60  
  Purchase #2 $147.89   11.433%   $164.7983   $164.80   $164.80   $164.80  
  Purchase #3 $91.83   5.193%   $96.5987   $96.60   $96.60   $96.60  
  Purchase #4 $36.69   3.322%   $37.9088   $37.91   $37.90   $37.90  
  Purchase #5 $75.93   5.579%   $80.1661   $80.17   $80.15   $80.20  
  Purchase #6 $182.50   12.398%   $205.1264   $205.13   $205.15   $205.10  
  Purchase #7 $159.92   6.165%   $169.7791   $169.78   $169.80   $169.80  
  7 purchase totals = $921.18       $1,006.9987   $1,007.01   $1,007.00   $1,007.00