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 $245.60   4.617%   $256.9394   $256.94   $256.95   $256.90  
  Purchase #2 $54.54   5.753%   $57.6777   $57.68   $57.70   $57.70  
  Purchase #3 $24.62   7.729%   $26.5229   $26.52   $26.50   $26.50  
  Purchase #4 $160.38   6.395%   $170.6363   $170.64   $170.65   $170.60  
  Purchase #5 $168.42   9.766%   $184.8679   $184.87   $184.85   $184.90  
  Purchase #6 $87.53   5.138%   $92.0273   $92.03   $92.05   $92.00  
  Purchase #7 $26.25   3.724%   $27.2276   $27.23   $27.25   $27.20  
  7 purchase totals = $767.34       $815.8991   $815.91   $815.95   $815.80