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 $236.79   11.788%   $264.7028   $264.70   $264.70   $264.70  
  Purchase #2 $137.47   4.730%   $143.9723   $143.97   $143.95   $144.00  
  Purchase #3 $148.67   11.218%   $165.3478   $165.35   $165.35   $165.30  
  Purchase #4 $58.65   3.819%   $60.8898   $60.89   $60.90   $60.90  
  Purchase #5 $117.52   6.330%   $124.959   $124.96   $124.95   $125.00  
  Purchase #6 $60.41   4.212%   $62.9545   $62.95   $62.95   $63.00  
  Purchase #7 $31.95   10.474%   $35.2964   $35.30   $35.30   $35.30  
  7 purchase totals = $791.46       $858.1226   $858.12   $858.10   $858.20