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 $122.69   9.763%   $134.6682   $134.67   $134.65   $134.70  
  Purchase #2 $53.29   3.132%   $54.959   $54.96   $54.95   $55.00  
  Purchase #3 $94.62   7.417%   $101.638   $101.64   $101.65   $101.60  
  Purchase #4 $34.67   3.570%   $35.9077   $35.91   $35.90   $35.90  
  Purchase #5 $23.41   7.638%   $25.1981   $25.20   $25.20   $25.20  
  Purchase #6 $97.85   10.158%   $107.7896   $107.79   $107.80   $107.80  
  Purchase #7 $41.34   9.354%   $45.2069   $45.21   $45.20   $45.20  
  7 purchase totals = $467.87       $505.3675   $505.38   $505.35   $505.40