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 $16.74   7.530%   $18.0005   $18.00   $18.00   $18.00  
  Purchase #2 $220.85   5.487%   $232.968   $232.97   $232.95   $233.00  
  Purchase #3 $131.72   5.735%   $139.2741   $139.27   $139.25   $139.30  
  Purchase #4 $101.42   4.349%   $105.8308   $105.83   $105.85   $105.80  
  Purchase #5 $9.77   13.198%   $11.0594   $11.06   $11.05   $11.10  
  Purchase #6 $179.97   4.253%   $187.6241   $187.62   $187.60   $187.60  
  Purchase #7 $40.26   7.736%   $43.3745   $43.37   $43.35   $43.40  
  7 purchase totals = $700.73       $738.1314   $738.12   $738.05   $738.20