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 $59.82   11.766%   $66.8584   $66.86   $66.85   $66.90  
  Purchase #2 $49.88   5.252%   $52.4997   $52.50   $52.50   $52.50  
  Purchase #3 $24.40   11.294%   $27.1557   $27.16   $27.15   $27.20  
  Purchase #4 $57.79   9.277%   $63.1512   $63.15   $63.15   $63.20  
  Purchase #5 $168.99   9.273%   $184.6604   $184.66   $184.65   $184.70  
  Purchase #6 $123.49   9.515%   $135.2401   $135.24   $135.25   $135.20  
  Purchase #7 $189.38   8.616%   $205.697   $205.70   $205.70   $205.70  
  7 purchase totals = $673.75       $735.2625   $735.27   $735.25   $735.40