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 $63.25   7.142%   $67.7673   $67.77   $67.75   $67.80  
  Purchase #2 $185.63   4.809%   $194.5569   $194.56   $194.55   $194.60  
  Purchase #3 $50.97   6.808%   $54.44   $54.44   $54.45   $54.40  
  Purchase #4 $196.25   7.422%   $210.8157   $210.82   $210.80   $210.80  
  Purchase #5 $22.52   3.192%   $23.2388   $23.24   $23.25   $23.20  
  Purchase #6 $204.77   10.115%   $225.4825   $225.48   $225.50   $225.50  
  Purchase #7 $31.42   12.699%   $35.41   $35.41   $35.40   $35.40  
  7 purchase totals = $754.81       $811.7112   $811.72   $811.70   $811.70