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 $246.78   7.366%   $264.9578   $264.96   $264.95   $265.00  
  Purchase #2 $134.51   10.196%   $148.2246   $148.22   $148.20   $148.20  
  Purchase #3 $217.35   4.464%   $227.0525   $227.05   $227.05   $227.10  
  Purchase #4 $46.99   6.342%   $49.9701   $49.97   $49.95   $50.00  
  Purchase #5 $97.48   12.809%   $109.9662   $109.97   $109.95   $110.00  
  Purchase #6 $19.66   6.376%   $20.9135   $20.91   $20.90   $20.90  
  Purchase #7 $232.31   5.625%   $245.3774   $245.38   $245.40   $245.40  
  7 purchase totals = $995.08       $1,066.4621   $1,066.46   $1,066.40   $1,066.60