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 $11.36   5.211%   $11.952   $11.95   $11.95   $12.00  
  Purchase #2 $32.86   4.596%   $34.3702   $34.37   $34.35   $34.40  
  Purchase #3 $83.53   11.295%   $92.9647   $92.96   $92.95   $93.00  
  Purchase #4 $141.29   9.645%   $154.9174   $154.92   $154.90   $154.90  
  Purchase #5 $227.49   7.426%   $244.3834   $244.38   $244.40   $244.40  
  Purchase #6 $73.85   5.729%   $78.0809   $78.08   $78.10   $78.10  
  Purchase #7 $33.26   10.198%   $36.6519   $36.65   $36.65   $36.70  
  7 purchase totals = $603.64       $653.3205   $653.31   $653.30   $653.50