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 $230.90   11.406%   $257.2365   $257.24   $257.25   $257.20  
  Purchase #2 $118.64   5.563%   $125.2399   $125.24   $125.25   $125.20  
  Purchase #3 $96.27   13.541%   $109.3059   $109.31   $109.30   $109.30  
  Purchase #4 $174.53   12.350%   $196.0845   $196.08   $196.10   $196.10  
  Purchase #5 $222.45   4.291%   $231.9953   $232.00   $232.00   $232.00  
  Purchase #6 $199.45   3.270%   $205.972   $205.97   $205.95   $206.00  
  Purchase #7 $110.79   10.561%   $122.4905   $122.49   $122.50   $122.50  
  7 purchase totals = $1,153.03       $1,248.3246   $1,248.33   $1,248.35   $1,248.30