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 $87.83   9.672%   $96.3249   $96.32   $96.30   $96.30  
  Purchase #2 $118.79   12.637%   $133.8015   $133.80   $133.80   $133.80  
  Purchase #3 $34.85   6.778%   $37.2121   $37.21   $37.20   $37.20  
  Purchase #4 $220.27   13.458%   $249.9139   $249.91   $249.90   $249.90  
  Purchase #5 $118.83   11.646%   $132.6689   $132.67   $132.65   $132.70  
  Purchase #6 $115.66   11.302%   $128.7319   $128.73   $128.75   $128.70  
  Purchase #7 $32.50   10.309%   $35.8504   $35.85   $35.85   $35.90  
  7 purchase totals = $728.73       $814.5036   $814.49   $814.45   $814.50