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 $98.38   6.699%   $104.9705   $104.97   $104.95   $105.00  
  Purchase #2 $65.68   4.676%   $68.7512   $68.75   $68.75   $68.80  
  Purchase #3 $23.26   6.330%   $24.7324   $24.73   $24.75   $24.70  
  Purchase #4 $162.96   4.643%   $170.5262   $170.53   $170.55   $170.50  
  Purchase #5 $183.71   4.124%   $191.2862   $191.29   $191.30   $191.30  
  Purchase #6 $10.78   5.312%   $11.3526   $11.35   $11.35   $11.40  
  Purchase #7 $167.59   5.306%   $176.4823   $176.48   $176.50   $176.50  
  7 purchase totals = $712.36       $748.1014   $748.10   $748.15   $748.20