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 $248.40   13.584%   $282.1427   $282.14   $282.15   $282.10  
  Purchase #2 $223.56   8.817%   $243.2713   $243.27   $243.25   $243.30  
  Purchase #3 $209.26   13.752%   $238.0374   $238.04   $238.05   $238.00  
  Purchase #4 $23.36   3.750%   $24.236   $24.24   $24.25   $24.20  
  Purchase #5 $88.41   7.822%   $95.3254   $95.33   $95.35   $95.30  
  Purchase #6 $98.45   9.807%   $108.105   $108.11   $108.10   $108.10  
  Purchase #7 $58.69   4.792%   $61.5024   $61.50   $61.50   $61.50  
  7 purchase totals = $950.13       $1,052.6202   $1,052.63   $1,052.65   $1,052.50