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 $105.59   11.121%   $117.3327   $117.33   $117.35   $117.30  
  Purchase #2 $196.30   3.366%   $202.9075   $202.91   $202.90   $202.90  
  Purchase #3 $171.70   5.163%   $180.5649   $180.56   $180.55   $180.60  
  Purchase #4 $59.95   10.558%   $66.2795   $66.28   $66.30   $66.30  
  Purchase #5 $243.99   12.871%   $275.394   $275.39   $275.40   $275.40  
  Purchase #6 $49.48   3.639%   $51.2806   $51.28   $51.30   $51.30  
  Purchase #7 $71.33   12.843%   $80.4909   $80.49   $80.50   $80.50  
  7 purchase totals = $898.34       $974.2501   $974.24   $974.30   $974.30