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 $59.77   9.451%   $65.4189   $65.42   $65.40   $65.40  
  Purchase #2 $191.95   6.156%   $203.7664   $203.77   $203.75   $203.80  
  Purchase #3 $145.92   8.677%   $158.5815   $158.58   $158.60   $158.60  
  Purchase #4 $50.41   10.431%   $55.6683   $55.67   $55.65   $55.70  
  Purchase #5 $114.54   9.865%   $125.8394   $125.84   $125.85   $125.80  
  Purchase #6 $139.59   6.127%   $148.1427   $148.14   $148.15   $148.10  
  Purchase #7 $26.81   4.574%   $28.0363   $28.04   $28.05   $28.00  
  7 purchase totals = $728.99       $785.4535   $785.46   $785.45   $785.40