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 $20.40   11.639%   $22.7744   $22.77   $22.75   $22.80  
  Purchase #2 $8.53   6.325%   $9.0695   $9.07   $9.05   $9.10  
  Purchase #3 $41.74   12.569%   $46.9863   $46.99   $47.00   $47.00  
  Purchase #4 $132.43   5.790%   $140.0977   $140.10   $140.10   $140.10  
  Purchase #5 $181.64   7.436%   $195.1468   $195.15   $195.15   $195.10  
  Purchase #6 $24.41   5.661%   $25.7919   $25.79   $25.80   $25.80  
  Purchase #7 $89.73   11.661%   $100.1934   $100.19   $100.20   $100.20  
  7 purchase totals = $498.88       $540.0600   $540.06   $540.05   $540.10