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 $182.48   13.799%   $207.6604   $207.66   $207.65   $207.70  
  Purchase #2 $10.98   7.590%   $11.8134   $11.81   $11.80   $11.80  
  Purchase #3 $180.54   8.192%   $195.3298   $195.33   $195.35   $195.30  
  Purchase #4 $24.25   3.230%   $25.0333   $25.03   $25.05   $25.00  
  Purchase #5 $221.35   3.779%   $229.7148   $229.71   $229.70   $229.70  
  Purchase #6 $5.56   9.531%   $6.0899   $6.09   $6.10   $6.10  
  Purchase #7 $242.72   5.536%   $256.157   $256.16   $256.15   $256.20  
  7 purchase totals = $867.88       $931.7986   $931.79   $931.80   $931.80