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 $187.38   11.713%   $209.3278   $209.33   $209.35   $209.30  
  Purchase #2 $92.67   3.499%   $95.9125   $95.91   $95.90   $95.90  
  Purchase #3 $33.36   5.778%   $35.2875   $35.29   $35.30   $35.30  
  Purchase #4 $101.92   8.386%   $110.467   $110.47   $110.45   $110.50  
  Purchase #5 $191.71   7.362%   $205.8237   $205.82   $205.80   $205.80  
  Purchase #6 $43.67   5.483%   $46.0644   $46.06   $46.05   $46.10  
  Purchase #7 $219.58   4.328%   $229.0834   $229.08   $229.10   $229.10  
  7 purchase totals = $870.29       $931.9663   $931.96   $931.95   $932.00