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 $162.76   13.438%   $184.6317   $184.63   $184.65   $184.60  
  Purchase #2 $221.66   10.765%   $245.5217   $245.52   $245.50   $245.50  
  Purchase #3 $28.77   4.348%   $30.0209   $30.02   $30.00   $30.00  
  Purchase #4 $223.88   8.520%   $242.9546   $242.95   $242.95   $243.00  
  Purchase #5 $51.95   11.476%   $57.9118   $57.91   $57.90   $57.90  
  Purchase #6 $40.67   11.677%   $45.419   $45.42   $45.40   $45.40  
  Purchase #7 $250.39   5.331%   $263.7383   $263.74   $263.75   $263.70  
  7 purchase totals = $980.08       $1,070.1980   $1,070.19   $1,070.15   $1,070.10