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 $93.94   13.193%   $106.3335   $106.33   $106.35   $106.30  
  Purchase #2 $204.62   11.404%   $227.9549   $227.95   $227.95   $228.00  
  Purchase #3 $24.77   12.835%   $27.9492   $27.95   $27.95   $27.90  
  Purchase #4 $24.71   12.210%   $27.7271   $27.73   $27.75   $27.70  
  Purchase #5 $46.37   4.333%   $48.3792   $48.38   $48.40   $48.40  
  Purchase #6 $193.45   7.610%   $208.1715   $208.17   $208.15   $208.20  
  Purchase #7 $163.79   13.430%   $185.787   $185.79   $185.80   $185.80  
  7 purchase totals = $751.65       $832.3024   $832.30   $832.35   $832.30