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 $152.54   13.158%   $172.6112   $172.61   $172.60   $172.60  
  Purchase #2 $74.92   12.111%   $83.9936   $83.99   $84.00   $84.00  
  Purchase #3 $153.30   6.362%   $163.0529   $163.05   $163.05   $163.10  
  Purchase #4 $154.74   7.408%   $166.2031   $166.20   $166.20   $166.20  
  Purchase #5 $8.97   13.493%   $10.1803   $10.18   $10.20   $10.20  
  Purchase #6 $14.81   9.450%   $16.2095   $16.21   $16.20   $16.20  
  Purchase #7 $25.38   5.496%   $26.7749   $26.77   $26.75   $26.80  
  7 purchase totals = $584.66       $639.0255   $639.01   $639.00   $639.10