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 $195.93   6.446%   $208.5596   $208.56   $208.55   $208.60  
  Purchase #2 $146.90   9.540%   $160.9143   $160.91   $160.90   $160.90  
  Purchase #3 $87.33   10.785%   $96.7485   $96.75   $96.75   $96.70  
  Purchase #4 $247.32   9.650%   $271.1864   $271.19   $271.20   $271.20  
  Purchase #5 $50.67   11.831%   $56.6648   $56.66   $56.65   $56.70  
  Purchase #6 $163.27   4.661%   $170.88   $170.88   $170.90   $170.90  
  Purchase #7 $65.82   8.177%   $71.2021   $71.20   $71.20   $71.20  
  7 purchase totals = $957.24       $1,036.1557   $1,036.15   $1,036.15   $1,036.20