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 $231.57   4.766%   $242.6066   $242.61   $242.60   $242.60  
  Purchase #2 $48.84   10.460%   $53.9487   $53.95   $53.95   $53.90  
  Purchase #3 $92.27   11.370%   $102.7611   $102.76   $102.75   $102.80  
  Purchase #4 $139.61   12.835%   $157.5289   $157.53   $157.55   $157.50  
  Purchase #5 $132.74   9.237%   $145.0012   $145.00   $145.00   $145.00  
  Purchase #6 $105.44   9.463%   $115.4178   $115.42   $115.40   $115.40  
  Purchase #7 $160.73   5.365%   $169.3532   $169.35   $169.35   $169.40  
  7 purchase totals = $911.20       $986.6175   $986.62   $986.60   $986.60