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 $163.83   7.226%   $175.6684   $175.67   $175.65   $175.70  
  Purchase #2 $186.72   9.426%   $204.3202   $204.32   $204.30   $204.30  
  Purchase #3 $208.81   9.175%   $227.9683   $227.97   $227.95   $228.00  
  Purchase #4 $175.51   10.690%   $194.272   $194.27   $194.25   $194.30  
  Purchase #5 $209.64   13.734%   $238.432   $238.43   $238.45   $238.40  
  Purchase #6 $86.34   8.144%   $93.3715   $93.37   $93.35   $93.40  
  Purchase #7 $131.98   12.555%   $148.5501   $148.55   $148.55   $148.60  
  7 purchase totals = $1,162.83       $1,282.5825   $1,282.58   $1,282.50   $1,282.70