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 $10.84   13.841%   $12.3404   $12.34   $12.35   $12.30  
  Purchase #2 $49.82   13.557%   $56.5741   $56.57   $56.55   $56.60  
  Purchase #3 $205.42   5.700%   $217.1289   $217.13   $217.15   $217.10  
  Purchase #4 $91.26   4.361%   $95.2398   $95.24   $95.25   $95.20  
  Purchase #5 $223.70   6.266%   $237.717   $237.72   $237.70   $237.70  
  Purchase #6 $87.71   7.415%   $94.2137   $94.21   $94.20   $94.20  
  Purchase #7 $57.29   5.518%   $60.4513   $60.45   $60.45   $60.50  
  7 purchase totals = $726.04       $773.6652   $773.66   $773.65   $773.60