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 $15.54   5.844%   $16.4482   $16.45   $16.45   $16.40  
  Purchase #2 $65.42   13.560%   $74.291   $74.29   $74.30   $74.30  
  Purchase #3 $174.29   8.862%   $189.7356   $189.74   $189.75   $189.70  
  Purchase #4 $170.89   5.293%   $179.9352   $179.94   $179.95   $179.90  
  Purchase #5 $36.38   10.290%   $40.1235   $40.12   $40.10   $40.10  
  Purchase #6 $22.67   12.161%   $25.4269   $25.43   $25.45   $25.40  
  Purchase #7 $93.33   6.463%   $99.3619   $99.36   $99.35   $99.40  
  7 purchase totals = $578.52       $625.3223   $625.33   $625.35   $625.20