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 $59.93   13.850%   $68.2303   $68.23   $68.25   $68.20  
  Purchase #2 $101.91   3.797%   $105.7795   $105.78   $105.80   $105.80  
  Purchase #3 $5.65   3.134%   $5.8271   $5.83   $5.85   $5.80  
  Purchase #4 $206.71   13.128%   $233.8469   $233.85   $233.85   $233.80  
  Purchase #5 $75.29   8.395%   $81.6106   $81.61   $81.60   $81.60  
  Purchase #6 $228.38   5.132%   $240.1005   $240.10   $240.10   $240.10  
  Purchase #7 $23.63   4.213%   $24.6255   $24.63   $24.65   $24.60  
  7 purchase totals = $701.50       $760.0204   $760.03   $760.10   $759.90