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 $119.73   10.122%   $131.8491   $131.85   $131.85   $131.80  
  Purchase #2 $57.29   9.834%   $62.9239   $62.92   $62.90   $62.90  
  Purchase #3 $165.63   9.478%   $181.3284   $181.33   $181.35   $181.30  
  Purchase #4 $249.82   6.555%   $266.1957   $266.20   $266.20   $266.20  
  Purchase #5 $14.45   3.402%   $14.9416   $14.94   $14.95   $14.90  
  Purchase #6 $145.47   8.464%   $157.7826   $157.78   $157.80   $157.80  
  Purchase #7 $59.38   4.473%   $62.0361   $62.04   $62.05   $62.00  
  7 purchase totals = $811.77       $877.0574   $877.06   $877.10   $876.90