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 $154.92   8.208%   $167.6358   $167.64   $167.65   $167.60  
  Purchase #2 $101.85   4.652%   $106.5881   $106.59   $106.60   $106.60  
  Purchase #3 $171.26   11.548%   $191.0371   $191.04   $191.05   $191.00  
  Purchase #4 $68.48   6.509%   $72.9374   $72.94   $72.95   $72.90  
  Purchase #5 $201.78   12.483%   $226.9682   $226.97   $226.95   $227.00  
  Purchase #6 $162.40   9.355%   $177.5925   $177.59   $177.60   $177.60  
  Purchase #7 $25.34   7.257%   $27.1789   $27.18   $27.20   $27.20  
  7 purchase totals = $886.03       $969.9380   $969.95   $970.00   $969.90