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 $53.77   9.186%   $58.7093   $58.71   $58.70   $58.70  
  Purchase #2 $244.44   5.527%   $257.9502   $257.95   $257.95   $258.00  
  Purchase #3 $31.86   10.609%   $35.24   $35.24   $35.25   $35.20  
  Purchase #4 $205.29   3.784%   $213.0582   $213.06   $213.05   $213.10  
  Purchase #5 $209.99   10.658%   $232.3707   $232.37   $232.35   $232.40  
  Purchase #6 $64.45   12.107%   $72.253   $72.25   $72.25   $72.30  
  Purchase #7 $113.37   11.367%   $126.2568   $126.26   $126.25   $126.30  
  7 purchase totals = $923.17       $995.8382   $995.84   $995.80   $996.00