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 $242.35   9.548%   $265.4896   $265.49   $265.50   $265.50  
  Purchase #2 $250.98   13.822%   $285.6705   $285.67   $285.65   $285.70  
  Purchase #3 $203.62   11.120%   $226.2625   $226.26   $226.25   $226.30  
  Purchase #4 $185.94   13.188%   $210.4618   $210.46   $210.45   $210.50  
  Purchase #5 $238.80   7.461%   $256.6169   $256.62   $256.60   $256.60  
  Purchase #6 $69.74   12.585%   $78.5168   $78.52   $78.50   $78.50  
  Purchase #7 $144.81   12.713%   $163.2197   $163.22   $163.20   $163.20  
  7 purchase totals = $1,336.24       $1,486.2378   $1,486.24   $1,486.15   $1,486.30