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 $58.57   9.182%   $63.9479   $63.95   $63.95   $63.90  
  Purchase #2 $201.57   12.809%   $227.3891   $227.39   $227.40   $227.40  
  Purchase #3 $84.31   13.873%   $96.0063   $96.01   $96.00   $96.00  
  Purchase #4 $147.79   9.130%   $161.2832   $161.28   $161.30   $161.30  
  Purchase #5 $110.84   10.569%   $122.5547   $122.55   $122.55   $122.60  
  Purchase #6 $152.42   7.561%   $163.9445   $163.94   $163.95   $163.90  
  Purchase #7 $118.31   6.452%   $125.9434   $125.94   $125.95   $125.90  
  7 purchase totals = $873.81       $961.0691   $961.06   $961.10   $961.00