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 $63.52   4.268%   $66.231   $66.23   $66.25   $66.20  
  Purchase #2 $120.69   6.702%   $128.7786   $128.78   $128.80   $128.80  
  Purchase #3 $10.63   11.695%   $11.8732   $11.87   $11.85   $11.90  
  Purchase #4 $195.81   9.142%   $213.711   $213.71   $213.70   $213.70  
  Purchase #5 $220.84   9.792%   $242.4647   $242.46   $242.45   $242.50  
  Purchase #6 $52.33   9.363%   $57.2297   $57.23   $57.25   $57.20  
  Purchase #7 $213.42   3.630%   $221.1671   $221.17   $221.15   $221.20  
  7 purchase totals = $877.24       $941.4553   $941.45   $941.45   $941.50