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 $65.71   8.431%   $71.25   $71.25   $71.25   $71.30  
  Purchase #2 $183.64   8.792%   $199.7856   $199.79   $199.80   $199.80  
  Purchase #3 $205.48   7.125%   $220.1205   $220.12   $220.10   $220.10  
  Purchase #4 $74.61   11.155%   $82.9327   $82.93   $82.95   $82.90  
  Purchase #5 $233.64   5.729%   $247.0252   $247.03   $247.05   $247.00  
  Purchase #6 $19.54   5.585%   $20.6313   $20.63   $20.65   $20.60  
  Purchase #7 $153.52   11.874%   $171.749   $171.75   $171.75   $171.70  
  7 purchase totals = $936.14       $1,013.4943   $1,013.50   $1,013.55   $1,013.40