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 $248.78   6.188%   $264.1745   $264.17   $264.15   $264.20  
  Purchase #2 $94.62   5.176%   $99.5175   $99.52   $99.50   $99.50  
  Purchase #3 $96.62   13.526%   $109.6888   $109.69   $109.70   $109.70  
  Purchase #4 $215.79   7.375%   $231.7045   $231.70   $231.70   $231.70  
  Purchase #5 $170.70   13.664%   $194.0244   $194.02   $194.00   $194.00  
  Purchase #6 $192.53   5.871%   $203.8334   $203.83   $203.85   $203.80  
  Purchase #7 $238.66   6.310%   $253.7194   $253.72   $253.70   $253.70  
  7 purchase totals = $1,257.70       $1,356.6625   $1,356.65   $1,356.60   $1,356.60