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 $151.48   10.183%   $166.9052   $166.91   $166.90   $166.90  
  Purchase #2 $84.54   13.329%   $95.8083   $95.81   $95.80   $95.80  
  Purchase #3 $145.61   13.431%   $165.1669   $165.17   $165.15   $165.20  
  Purchase #4 $69.56   10.553%   $76.9007   $76.90   $76.90   $76.90  
  Purchase #5 $169.95   11.640%   $189.7322   $189.73   $189.75   $189.70  
  Purchase #6 $249.93   6.603%   $266.4329   $266.43   $266.45   $266.40  
  Purchase #7 $32.32   8.331%   $35.0126   $35.01   $35.00   $35.00  
  7 purchase totals = $903.39       $995.9588   $995.96   $995.95   $995.90