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 $51.43   4.275%   $53.6286   $53.63   $53.65   $53.60  
  Purchase #2 $219.50   3.117%   $226.3418   $226.34   $226.35   $226.30  
  Purchase #3 $212.55   12.374%   $238.8509   $238.85   $238.85   $238.90  
  Purchase #4 $65.86   5.851%   $69.7135   $69.71   $69.70   $69.70  
  Purchase #5 $67.66   9.557%   $74.1263   $74.13   $74.15   $74.10  
  Purchase #6 $223.33   11.450%   $248.9013   $248.90   $248.90   $248.90  
  Purchase #7 $77.65   6.428%   $82.6413   $82.64   $82.65   $82.60  
  7 purchase totals = $917.98       $994.2037   $994.20   $994.25   $994.10