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 $206.71   12.868%   $233.3094   $233.31   $233.30   $233.30  
  Purchase #2 $22.60   9.598%   $24.7691   $24.77   $24.75   $24.80  
  Purchase #3 $137.90   13.847%   $156.995   $157.00   $157.00   $157.00  
  Purchase #4 $77.35   10.334%   $85.3433   $85.34   $85.35   $85.30  
  Purchase #5 $212.53   11.826%   $237.6638   $237.66   $237.65   $237.70  
  Purchase #6 $225.60   7.440%   $242.3846   $242.38   $242.40   $242.40  
  Purchase #7 $29.55   9.698%   $32.4158   $32.42   $32.40   $32.40  
  7 purchase totals = $912.24       $1,012.8810   $1,012.88   $1,012.85   $1,012.90