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 $245.41   4.309%   $255.9847   $255.98   $256.00   $256.00  
  Purchase #2 $66.65   12.229%   $74.8006   $74.80   $74.80   $74.80  
  Purchase #3 $59.89   7.644%   $64.468   $64.47   $64.45   $64.50  
  Purchase #4 $116.58   12.432%   $131.0732   $131.07   $131.05   $131.10  
  Purchase #5 $186.76   11.302%   $207.8676   $207.87   $207.85   $207.90  
  Purchase #6 $69.49   10.602%   $76.8573   $76.86   $76.85   $76.90  
  Purchase #7 $233.40   10.313%   $257.4705   $257.47   $257.45   $257.50  
  7 purchase totals = $978.18       $1,068.5219   $1,068.52   $1,068.45   $1,068.70