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 $249.78   11.127%   $277.573   $277.57   $277.55   $277.60  
  Purchase #2 $44.25   6.615%   $47.1771   $47.18   $47.20   $47.20  
  Purchase #3 $67.89   4.587%   $71.0041   $71.00   $71.00   $71.00  
  Purchase #4 $10.67   5.157%   $11.2203   $11.22   $11.20   $11.20  
  Purchase #5 $152.44   9.526%   $166.9614   $166.96   $166.95   $167.00  
  Purchase #6 $53.92   13.562%   $61.2326   $61.23   $61.25   $61.20  
  Purchase #7 $104.33   6.858%   $111.485   $111.49   $111.50   $111.50  
  7 purchase totals = $683.28       $746.6535   $746.65   $746.65   $746.70