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 $56.78   11.760%   $63.4573   $63.46   $63.45   $63.50  
  Purchase #2 $102.36   8.199%   $110.7525   $110.75   $110.75   $110.80  
  Purchase #3 $59.55   5.468%   $62.8062   $62.81   $62.80   $62.80  
  Purchase #4 $220.69   4.751%   $231.175   $231.18   $231.20   $231.20  
  Purchase #5 $134.79   10.441%   $148.8634   $148.86   $148.85   $148.90  
  Purchase #6 $139.80   8.864%   $152.1919   $152.19   $152.20   $152.20  
  Purchase #7 $196.98   5.234%   $207.2899   $207.29   $207.30   $207.30  
  7 purchase totals = $910.95       $976.5362   $976.54   $976.55   $976.70