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 $232.81   9.443%   $254.7942   $254.79   $254.80   $254.80  
  Purchase #2 $207.58   11.128%   $230.6795   $230.68   $230.70   $230.70  
  Purchase #3 $53.87   11.737%   $60.1927   $60.19   $60.20   $60.20  
  Purchase #4 $240.90   11.238%   $267.9723   $267.97   $267.95   $268.00  
  Purchase #5 $171.96   5.659%   $181.6912   $181.69   $181.70   $181.70  
  Purchase #6 $120.78   10.260%   $133.172   $133.17   $133.15   $133.20  
  Purchase #7 $130.63   6.576%   $139.2202   $139.22   $139.20   $139.20  
  7 purchase totals = $1,158.53       $1,267.7221   $1,267.71   $1,267.70   $1,267.80