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 $49.30   9.283%   $53.8765   $53.88   $53.90   $53.90  
  Purchase #2 $58.67   3.852%   $60.93   $60.93   $60.95   $60.90  
  Purchase #3 $56.53   5.537%   $59.6601   $59.66   $59.65   $59.70  
  Purchase #4 $207.89   11.348%   $231.4814   $231.48   $231.50   $231.50  
  Purchase #5 $65.62   5.669%   $69.34   $69.34   $69.35   $69.30  
  Purchase #6 $40.30   13.844%   $45.8791   $45.88   $45.90   $45.90  
  Purchase #7 $216.59   5.704%   $228.9443   $228.94   $228.95   $228.90  
  7 purchase totals = $694.90       $750.1114   $750.11   $750.20   $750.10