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 $59.84   3.146%   $61.7226   $61.72   $61.70   $61.70  
  Purchase #2 $9.44   4.136%   $9.8304   $9.83   $9.85   $9.80  
  Purchase #3 $205.39   4.422%   $214.4723   $214.47   $214.45   $214.50  
  Purchase #4 $101.86   8.205%   $110.2176   $110.22   $110.20   $110.20  
  Purchase #5 $98.50   12.556%   $110.8677   $110.87   $110.85   $110.90  
  Purchase #6 $189.49   9.514%   $207.5181   $207.52   $207.50   $207.50  
  Purchase #7 $142.68   7.491%   $153.3682   $153.37   $153.35   $153.40  
  7 purchase totals = $807.20       $867.9969   $868.00   $867.90   $868.00