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 $35.94   12.407%   $40.3991   $40.40   $40.40   $40.40  
  Purchase #2 $232.81   4.719%   $243.7963   $243.80   $243.80   $243.80  
  Purchase #3 $119.92   5.595%   $126.6295   $126.63   $126.65   $126.60  
  Purchase #4 $182.61   6.440%   $194.3701   $194.37   $194.35   $194.40  
  Purchase #5 $103.51   11.304%   $115.2108   $115.21   $115.20   $115.20  
  Purchase #6 $230.96   7.206%   $247.603   $247.60   $247.60   $247.60  
  Purchase #7 $7.65   9.270%   $8.3592   $8.36   $8.35   $8.40  
  7 purchase totals = $913.40       $976.3680   $976.37   $976.35   $976.40