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 $223.80   5.253%   $235.5562   $235.56   $235.55   $235.60  
  Purchase #2 $12.68   10.474%   $14.0081   $14.01   $14.00   $14.00  
  Purchase #3 $233.51   12.579%   $262.8832   $262.88   $262.90   $262.90  
  Purchase #4 $149.65   7.522%   $160.9067   $160.91   $160.90   $160.90  
  Purchase #5 $172.72   3.860%   $179.387   $179.39   $179.40   $179.40  
  Purchase #6 $69.61   11.746%   $77.7864   $77.79   $77.80   $77.80  
  Purchase #7 $23.63   7.502%   $25.4027   $25.40   $25.40   $25.40  
  7 purchase totals = $885.60       $955.9303   $955.94   $955.95   $956.00