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 $68.94   6.739%   $73.5859   $73.59   $73.60   $73.60  
  Purchase #2 $133.90   13.567%   $152.0662   $152.07   $152.05   $152.10  
  Purchase #3 $95.97   8.395%   $104.0267   $104.03   $104.05   $104.00  
  Purchase #4 $170.82   10.826%   $189.313   $189.31   $189.30   $189.30  
  Purchase #5 $108.56   8.859%   $118.1773   $118.18   $118.20   $118.20  
  Purchase #6 $233.90   7.728%   $251.9758   $251.98   $252.00   $252.00  
  Purchase #7 $176.64   8.148%   $191.0326   $191.03   $191.05   $191.00  
  7 purchase totals = $988.73       $1,080.1775   $1,080.19   $1,080.25   $1,080.20