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 $91.89   5.207%   $96.6747   $96.67   $96.65   $96.70  
  Purchase #2 $129.71   12.646%   $146.1131   $146.11   $146.10   $146.10  
  Purchase #3 $116.82   13.677%   $132.7975   $132.80   $132.80   $132.80  
  Purchase #4 $80.89   12.682%   $91.1485   $91.15   $91.15   $91.10  
  Purchase #5 $112.79   6.797%   $120.4563   $120.46   $120.45   $120.50  
  Purchase #6 $206.88   3.774%   $214.6877   $214.69   $214.70   $214.70  
  Purchase #7 $29.43   7.544%   $31.6502   $31.65   $31.65   $31.70  
  7 purchase totals = $768.41       $833.5280   $833.53   $833.50   $833.60