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 $55.83   5.755%   $59.043   $59.04   $59.05   $59.00  
  Purchase #2 $239.93   6.564%   $255.679   $255.68   $255.70   $255.70  
  Purchase #3 $101.68   6.810%   $108.6044   $108.60   $108.60   $108.60  
  Purchase #4 $69.62   9.204%   $76.0278   $76.03   $76.05   $76.00  
  Purchase #5 $178.36   4.575%   $186.52   $186.52   $186.50   $186.50  
  Purchase #6 $50.91   5.515%   $53.7177   $53.72   $53.70   $53.70  
  Purchase #7 $120.67   3.748%   $125.1927   $125.19   $125.20   $125.20  
  7 purchase totals = $817.00       $864.7846   $864.78   $864.80   $864.70