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 $45.88   13.246%   $51.9573   $51.96   $51.95   $52.00  
  Purchase #2 $228.83   7.571%   $246.1547   $246.15   $246.15   $246.20  
  Purchase #3 $209.59   13.368%   $237.608   $237.61   $237.60   $237.60  
  Purchase #4 $25.84   13.196%   $29.2498   $29.25   $29.25   $29.20  
  Purchase #5 $67.53   12.122%   $75.716   $75.72   $75.70   $75.70  
  Purchase #6 $20.76   13.734%   $23.6112   $23.61   $23.60   $23.60  
  Purchase #7 $193.38   4.363%   $201.8172   $201.82   $201.80   $201.80  
  7 purchase totals = $791.81       $866.1142   $866.12   $866.05   $866.10