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 $117.82   7.639%   $126.8203   $126.82   $126.80   $126.80  
  Purchase #2 $232.40   13.599%   $264.0041   $264.00   $264.00   $264.00  
  Purchase #3 $25.94   3.716%   $26.9039   $26.90   $26.90   $26.90  
  Purchase #4 $16.39   11.828%   $18.3286   $18.33   $18.35   $18.30  
  Purchase #5 $73.86   10.187%   $81.3841   $81.38   $81.40   $81.40  
  Purchase #6 $102.46   8.380%   $111.0461   $111.05   $111.05   $111.00  
  Purchase #7 $236.69   4.172%   $246.5647   $246.56   $246.55   $246.60  
  7 purchase totals = $805.56       $875.0518   $875.04   $875.05   $875.00