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 $74.49   10.104%   $82.0165   $82.02   $82.00   $82.00  
  Purchase #2 $59.68   6.284%   $63.4303   $63.43   $63.45   $63.40  
  Purchase #3 $148.46   3.330%   $153.4037   $153.40   $153.40   $153.40  
  Purchase #4 $166.86   5.319%   $175.7353   $175.74   $175.75   $175.70  
  Purchase #5 $54.31   4.130%   $56.553   $56.55   $56.55   $56.60  
  Purchase #6 $241.55   7.557%   $259.8039   $259.80   $259.80   $259.80  
  Purchase #7 $136.94   3.351%   $141.5289   $141.53   $141.55   $141.50  
  7 purchase totals = $882.29       $932.4716   $932.47   $932.50   $932.40