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 $54.94   4.846%   $57.6024   $57.60   $57.60   $57.60  
  Purchase #2 $209.61   9.356%   $229.2211   $229.22   $229.20   $229.20  
  Purchase #3 $160.97   3.407%   $166.4542   $166.45   $166.45   $166.50  
  Purchase #4 $46.60   10.415%   $51.4534   $51.45   $51.45   $51.50  
  Purchase #5 $157.58   6.190%   $167.3342   $167.33   $167.35   $167.30  
  Purchase #6 $36.42   13.437%   $41.3138   $41.31   $41.30   $41.30  
  Purchase #7 $26.76   4.795%   $28.0431   $28.04   $28.05   $28.00  
  7 purchase totals = $692.88       $741.4222   $741.40   $741.40   $741.40