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 $167.42   11.309%   $186.3535   $186.35   $186.35   $186.40  
  Purchase #2 $125.98   8.677%   $136.9113   $136.91   $136.90   $136.90  
  Purchase #3 $20.60   12.496%   $23.1742   $23.17   $23.15   $23.20  
  Purchase #4 $92.73   13.129%   $104.9045   $104.90   $104.90   $104.90  
  Purchase #5 $250.48   3.510%   $259.2718   $259.27   $259.25   $259.30  
  Purchase #6 $94.25   3.142%   $97.2113   $97.21   $97.20   $97.20  
  Purchase #7 $243.30   10.723%   $269.3891   $269.39   $269.40   $269.40  
  7 purchase totals = $994.76       $1,077.2157   $1,077.20   $1,077.15   $1,077.30