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 $58.95   12.239%   $66.1649   $66.16   $66.15   $66.20  
  Purchase #2 $196.48   4.170%   $204.6732   $204.67   $204.65   $204.70  
  Purchase #3 $20.89   6.710%   $22.2917   $22.29   $22.30   $22.30  
  Purchase #4 $63.80   9.755%   $70.0237   $70.02   $70.00   $70.00  
  Purchase #5 $86.80   7.501%   $93.3109   $93.31   $93.30   $93.30  
  Purchase #6 $244.51   9.329%   $267.3203   $267.32   $267.30   $267.30  
  Purchase #7 $103.61   5.142%   $108.9376   $108.94   $108.95   $108.90  
  7 purchase totals = $775.04       $832.7223   $832.71   $832.65   $832.70