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 $105.37   5.467%   $111.1306   $111.13   $111.15   $111.10  
  Purchase #2 $210.42   8.421%   $228.1395   $228.14   $228.15   $228.10  
  Purchase #3 $141.41   3.704%   $146.6478   $146.65   $146.65   $146.60  
  Purchase #4 $6.32   13.652%   $7.1828   $7.18   $7.20   $7.20  
  Purchase #5 $119.82   5.728%   $126.6833   $126.68   $126.70   $126.70  
  Purchase #6 $125.55   7.435%   $134.8846   $134.88   $134.90   $134.90  
  Purchase #7 $99.68   9.302%   $108.9522   $108.95   $108.95   $109.00  
  7 purchase totals = $808.57       $863.6208   $863.61   $863.70   $863.60