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 $73.68   8.580%   $80.0017   $80.00   $80.00   $80.00  
  Purchase #2 $89.65   6.483%   $95.462   $95.46   $95.45   $95.50  
  Purchase #3 $177.93   6.564%   $189.6093   $189.61   $189.60   $189.60  
  Purchase #4 $176.42   6.742%   $188.3142   $188.31   $188.30   $188.30  
  Purchase #5 $102.56   12.125%   $114.9954   $115.00   $115.00   $115.00  
  Purchase #6 $97.99   6.302%   $104.1653   $104.17   $104.15   $104.20  
  Purchase #7 $157.55   7.418%   $169.2371   $169.24   $169.25   $169.20  
  7 purchase totals = $875.78       $941.7850   $941.79   $941.75   $941.80