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 $56.25   13.276%   $63.7178   $63.72   $63.70   $63.70  
  Purchase #2 $107.58   8.148%   $116.3456   $116.35   $116.35   $116.30  
  Purchase #3 $5.46   5.794%   $5.7764   $5.78   $5.80   $5.80  
  Purchase #4 $148.76   11.846%   $166.3821   $166.38   $166.40   $166.40  
  Purchase #5 $88.63   7.405%   $95.1931   $95.19   $95.20   $95.20  
  Purchase #6 $180.81   5.209%   $190.2284   $190.23   $190.25   $190.20  
  Purchase #7 $159.87   12.151%   $179.2958   $179.30   $179.30   $179.30  
  7 purchase totals = $747.36       $816.9392   $816.95   $817.00   $816.90