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 $208.98   9.559%   $228.9564   $228.96   $228.95   $229.00  
  Purchase #2 $181.59   7.743%   $195.6505   $195.65   $195.65   $195.70  
  Purchase #3 $178.50   9.590%   $195.6182   $195.62   $195.60   $195.60  
  Purchase #4 $42.97   5.192%   $45.201   $45.20   $45.20   $45.20  
  Purchase #5 $89.84   9.766%   $98.6138   $98.61   $98.60   $98.60  
  Purchase #6 $143.52   12.641%   $161.6624   $161.66   $161.65   $161.70  
  Purchase #7 $124.87   4.732%   $130.7788   $130.78   $130.80   $130.80  
  7 purchase totals = $970.27       $1,056.4811   $1,056.48   $1,056.45   $1,056.60