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 $56.26   6.179%   $59.7363   $59.74   $59.75   $59.70  
  Purchase #2 $238.75   7.553%   $256.7828   $256.78   $256.80   $256.80  
  Purchase #3 $46.82   11.672%   $52.2848   $52.28   $52.30   $52.30  
  Purchase #4 $201.26   13.113%   $227.6512   $227.65   $227.65   $227.70  
  Purchase #5 $203.48   5.465%   $214.6002   $214.60   $214.60   $214.60  
  Purchase #6 $112.25   10.868%   $124.4493   $124.45   $124.45   $124.40  
  Purchase #7 $87.78   4.687%   $91.8942   $91.89   $91.90   $91.90  
  7 purchase totals = $946.60       $1,027.3988   $1,027.39   $1,027.45   $1,027.40