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 $97.40   8.397%   $105.5787   $105.58   $105.60   $105.60  
  Purchase #2 $180.93   13.715%   $205.7445   $205.74   $205.75   $205.70  
  Purchase #3 $9.26   10.567%   $10.2385   $10.24   $10.25   $10.20  
  Purchase #4 $63.92   13.657%   $72.6496   $72.65   $72.65   $72.60  
  Purchase #5 $91.78   7.823%   $98.9599   $98.96   $98.95   $99.00  
  Purchase #6 $227.36   6.329%   $241.7496   $241.75   $241.75   $241.70  
  Purchase #7 $194.93   6.289%   $207.1891   $207.19   $207.20   $207.20  
  7 purchase totals = $865.58       $942.1099   $942.11   $942.15   $942.00