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 $184.80   9.731%   $202.7829   $202.78   $202.80   $202.80  
  Purchase #2 $31.97   8.311%   $34.627   $34.63   $34.65   $34.60  
  Purchase #3 $138.47   3.773%   $143.6945   $143.69   $143.70   $143.70  
  Purchase #4 $15.43   4.494%   $16.1234   $16.12   $16.10   $16.10  
  Purchase #5 $148.60   8.819%   $161.705   $161.71   $161.70   $161.70  
  Purchase #6 $64.25   11.133%   $71.403   $71.40   $71.40   $71.40  
  Purchase #7 $214.32   8.661%   $232.8823   $232.88   $232.90   $232.90  
  7 purchase totals = $797.84       $863.2181   $863.21   $863.25   $863.20