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 $56.46   10.242%   $62.2426   $62.24   $62.25   $62.20  
  Purchase #2 $92.38   9.159%   $100.8411   $100.84   $100.85   $100.80  
  Purchase #3 $5.48   8.682%   $5.9558   $5.96   $5.95   $6.00  
  Purchase #4 $200.47   9.672%   $219.8595   $219.86   $219.85   $219.90  
  Purchase #5 $207.33   6.769%   $221.3642   $221.36   $221.35   $221.40  
  Purchase #6 $163.80   12.334%   $184.0031   $184.00   $184.00   $184.00  
  Purchase #7 $162.32   10.218%   $178.9059   $178.91   $178.90   $178.90  
  7 purchase totals = $888.24       $973.1722   $973.17   $973.15   $973.20