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 $219.35   8.698%   $238.4291   $238.43   $238.45   $238.40  
  Purchase #2 $60.39   5.418%   $63.6619   $63.66   $63.65   $63.70  
  Purchase #3 $172.26   8.494%   $186.8918   $186.89   $186.90   $186.90  
  Purchase #4 $26.34   8.398%   $28.552   $28.55   $28.55   $28.60  
  Purchase #5 $156.97   12.420%   $176.4657   $176.47   $176.45   $176.50  
  Purchase #6 $40.94   9.132%   $44.6786   $44.68   $44.70   $44.70  
  Purchase #7 $52.63   7.397%   $56.523   $56.52   $56.50   $56.50  
  7 purchase totals = $728.88       $795.2021   $795.20   $795.20   $795.30