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 $62.81   9.363%   $68.6909   $68.69   $68.70   $68.70  
  Purchase #2 $26.54   13.357%   $30.0849   $30.08   $30.10   $30.10  
  Purchase #3 $153.25   8.203%   $165.8211   $165.82   $165.80   $165.80  
  Purchase #4 $41.71   9.598%   $45.7133   $45.71   $45.70   $45.70  
  Purchase #5 $145.81   9.159%   $159.1647   $159.16   $159.15   $159.20  
  Purchase #6 $221.49   4.452%   $231.3507   $231.35   $231.35   $231.40  
  Purchase #7 $29.31   10.605%   $32.4183   $32.42   $32.40   $32.40  
  7 purchase totals = $680.92       $733.2439   $733.23   $733.20   $733.30