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 $155.53   7.865%   $167.7624   $167.76   $167.75   $167.80  
  Purchase #2 $213.34   9.383%   $233.3577   $233.36   $233.35   $233.40  
  Purchase #3 $13.98   7.250%   $14.9936   $14.99   $15.00   $15.00  
  Purchase #4 $135.92   10.190%   $149.7702   $149.77   $149.75   $149.80  
  Purchase #5 $71.82   6.284%   $76.3332   $76.33   $76.35   $76.30  
  Purchase #6 $25.88   6.292%   $27.5084   $27.51   $27.50   $27.50  
  Purchase #7 $58.74   10.224%   $64.7456   $64.75   $64.75   $64.70  
  7 purchase totals = $675.21       $734.4711   $734.47   $734.45   $734.50