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 $83.67   9.336%   $91.4814   $91.48   $91.50   $91.50  
  Purchase #2 $192.66   5.694%   $203.6301   $203.63   $203.65   $203.60  
  Purchase #3 $17.74   13.373%   $20.1124   $20.11   $20.10   $20.10  
  Purchase #4 $230.29   8.466%   $249.7864   $249.79   $249.80   $249.80  
  Purchase #5 $107.95   5.400%   $113.7793   $113.78   $113.80   $113.80  
  Purchase #6 $221.80   10.144%   $244.2994   $244.30   $244.30   $244.30  
  Purchase #7 $91.78   10.586%   $101.4958   $101.50   $101.50   $101.50  
  7 purchase totals = $945.89       $1,024.5848   $1,024.59   $1,024.65   $1,024.60