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 $95.93   10.801%   $106.2914   $106.29   $106.30   $106.30  
  Purchase #2 $56.69   13.441%   $64.3097   $64.31   $64.30   $64.30  
  Purchase #3 $155.94   3.689%   $161.6926   $161.69   $161.70   $161.70  
  Purchase #4 $32.93   6.492%   $35.0678   $35.07   $35.05   $35.10  
  Purchase #5 $140.29   13.343%   $159.0089   $159.01   $159.00   $159.00  
  Purchase #6 $233.51   12.204%   $262.0076   $262.01   $262.00   $262.00  
  Purchase #7 $224.47   12.804%   $253.2111   $253.21   $253.20   $253.20  
  7 purchase totals = $939.76       $1,041.5891   $1,041.59   $1,041.55   $1,041.60