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 $162.96   8.437%   $176.7089   $176.71   $176.70   $176.70  
  Purchase #2 $147.50   7.762%   $158.949   $158.95   $158.95   $158.90  
  Purchase #3 $158.42   10.535%   $175.1095   $175.11   $175.10   $175.10  
  Purchase #4 $98.34   6.615%   $104.8452   $104.85   $104.85   $104.80  
  Purchase #5 $150.93   7.717%   $162.5773   $162.58   $162.60   $162.60  
  Purchase #6 $82.88   6.384%   $88.1711   $88.17   $88.15   $88.20  
  Purchase #7 $76.41   5.566%   $80.663   $80.66   $80.65   $80.70  
  7 purchase totals = $877.44       $947.0240   $947.03   $947.00   $947.00