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 $83.98   11.527%   $93.6604   $93.66   $93.65   $93.70  
  Purchase #2 $228.67   4.855%   $239.7719   $239.77   $239.75   $239.80  
  Purchase #3 $72.85   7.578%   $78.3706   $78.37   $78.35   $78.40  
  Purchase #4 $61.52   3.477%   $63.6591   $63.66   $63.65   $63.70  
  Purchase #5 $128.78   13.253%   $145.8472   $145.85   $145.85   $145.80  
  Purchase #6 $152.30   5.344%   $160.4389   $160.44   $160.45   $160.40  
  Purchase #7 $78.93   5.365%   $83.1646   $83.16   $83.15   $83.20  
  7 purchase totals = $807.03       $864.9127   $864.91   $864.85   $865.00