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 $44.53   13.317%   $50.4601   $50.46   $50.45   $50.50  
  Purchase #2 $207.52   13.695%   $235.9399   $235.94   $235.95   $235.90  
  Purchase #3 $216.95   3.661%   $224.8925   $224.89   $224.90   $224.90  
  Purchase #4 $156.74   3.288%   $161.8936   $161.89   $161.90   $161.90  
  Purchase #5 $226.29   12.603%   $254.8093   $254.81   $254.80   $254.80  
  Purchase #6 $77.82   9.849%   $85.4845   $85.48   $85.50   $85.50  
  Purchase #7 $23.49   4.511%   $24.5496   $24.55   $24.55   $24.50  
  7 purchase totals = $953.34       $1,038.0295   $1,038.02   $1,038.05   $1,038.00