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 $61.39   13.110%   $69.4382   $69.44   $69.45   $69.40  
  Purchase #2 $188.74   12.352%   $212.0532   $212.05   $212.05   $212.10  
  Purchase #3 $26.69   10.197%   $29.4116   $29.41   $29.40   $29.40  
  Purchase #4 $62.44   3.777%   $64.7984   $64.80   $64.80   $64.80  
  Purchase #5 $218.80   12.778%   $246.7583   $246.76   $246.75   $246.80  
  Purchase #6 $153.87   9.443%   $168.3999   $168.40   $168.40   $168.40  
  Purchase #7 $66.43   13.503%   $75.4   $75.40   $75.40   $75.40  
  7 purchase totals = $778.36       $866.2596   $866.26   $866.25   $866.30