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 $94.75   4.833%   $99.3293   $99.33   $99.35   $99.30  
  Purchase #2 $127.78   6.433%   $136.0001   $136.00   $136.00   $136.00  
  Purchase #3 $100.37   12.634%   $113.0507   $113.05   $113.05   $113.10  
  Purchase #4 $52.92   9.756%   $58.0829   $58.08   $58.10   $58.10  
  Purchase #5 $197.62   7.282%   $212.0107   $212.01   $212.00   $212.00  
  Purchase #6 $66.95   7.822%   $72.1868   $72.19   $72.20   $72.20  
  Purchase #7 $238.36   10.470%   $263.3163   $263.32   $263.30   $263.30  
  7 purchase totals = $878.75       $953.9768   $953.98   $954.00   $954.00