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 $163.58   6.541%   $174.2798   $174.28   $174.30   $174.30  
  Purchase #2 $85.49   9.184%   $93.3414   $93.34   $93.35   $93.30  
  Purchase #3 $79.35   11.143%   $88.192   $88.19   $88.20   $88.20  
  Purchase #4 $62.30   13.643%   $70.7996   $70.80   $70.80   $70.80  
  Purchase #5 $205.37   10.148%   $226.2109   $226.21   $226.20   $226.20  
  Purchase #6 $151.87   12.771%   $171.2653   $171.27   $171.25   $171.30  
  Purchase #7 $101.33   10.381%   $111.8491   $111.85   $111.85   $111.80  
  7 purchase totals = $849.29       $935.9381   $935.94   $935.95   $935.90