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 $109.67   6.263%   $116.5386   $116.54   $116.55   $116.50  
  Purchase #2 $33.57   3.299%   $34.6775   $34.68   $34.70   $34.70  
  Purchase #3 $7.28   10.465%   $8.0419   $8.04   $8.05   $8.00  
  Purchase #4 $162.88   6.596%   $173.6236   $173.62   $173.60   $173.60  
  Purchase #5 $175.62   5.807%   $185.8183   $185.82   $185.80   $185.80  
  Purchase #6 $75.80   5.814%   $80.207   $80.21   $80.20   $80.20  
  Purchase #7 $183.32   9.213%   $200.2093   $200.21   $200.20   $200.20  
  7 purchase totals = $748.14       $799.1162   $799.12   $799.10   $799.00