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 $20.64   11.579%   $23.0299   $23.03   $23.05   $23.00  
  Purchase #2 $99.76   13.488%   $113.2156   $113.22   $113.20   $113.20  
  Purchase #3 $62.82   9.179%   $68.5862   $68.59   $68.60   $68.60  
  Purchase #4 $201.59   12.623%   $227.0367   $227.04   $227.05   $227.00  
  Purchase #5 $31.46   4.413%   $32.8483   $32.85   $32.85   $32.80  
  Purchase #6 $124.93   5.868%   $132.2609   $132.26   $132.25   $132.30  
  Purchase #7 $126.96   12.333%   $142.618   $142.62   $142.60   $142.60  
  7 purchase totals = $668.16       $739.5956   $739.61   $739.60   $739.50