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 $90.38   12.681%   $101.8411   $101.84   $101.85   $101.80  
  Purchase #2 $18.27   6.333%   $19.427   $19.43   $19.45   $19.40  
  Purchase #3 $192.76   12.464%   $216.7856   $216.79   $216.80   $216.80  
  Purchase #4 $206.87   11.717%   $231.109   $231.11   $231.10   $231.10  
  Purchase #5 $133.53   11.498%   $148.8833   $148.88   $148.90   $148.90  
  Purchase #6 $212.59   9.351%   $232.4693   $232.47   $232.45   $232.50  
  Purchase #7 $108.87   6.679%   $116.1414   $116.14   $116.15   $116.10  
  7 purchase totals = $963.27       $1,066.6567   $1,066.66   $1,066.70   $1,066.60