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 $55.62   13.290%   $63.0119   $63.01   $63.00   $63.00  
  Purchase #2 $127.96   9.389%   $139.9742   $139.97   $139.95   $140.00  
  Purchase #3 $29.45   13.262%   $33.3557   $33.36   $33.35   $33.40  
  Purchase #4 $166.36   4.643%   $174.0841   $174.08   $174.10   $174.10  
  Purchase #5 $120.91   11.558%   $134.8848   $134.88   $134.90   $134.90  
  Purchase #6 $158.31   9.723%   $173.7025   $173.70   $173.70   $173.70  
  Purchase #7 $9.85   10.698%   $10.9038   $10.90   $10.90   $10.90  
  7 purchase totals = $668.46       $729.9170   $729.90   $729.90   $730.00