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 $64.78   6.792%   $69.1799   $69.18   $69.20   $69.20  
  Purchase #2 $229.43   5.175%   $241.303   $241.30   $241.30   $241.30  
  Purchase #3 $104.97   8.407%   $113.7948   $113.79   $113.80   $113.80  
  Purchase #4 $176.64   8.588%   $191.8098   $191.81   $191.80   $191.80  
  Purchase #5 $205.47   10.831%   $227.7245   $227.72   $227.70   $227.70  
  Purchase #6 $43.95   11.451%   $48.9827   $48.98   $49.00   $49.00  
  Purchase #7 $71.50   4.172%   $74.483   $74.48   $74.50   $74.50  
  7 purchase totals = $896.74       $967.2777   $967.26   $967.30   $967.30