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 $162.89   11.682%   $181.9188   $181.92   $181.90   $181.90  
  Purchase #2 $178.33   8.202%   $192.9566   $192.96   $192.95   $193.00  
  Purchase #3 $75.55   10.173%   $83.2357   $83.24   $83.25   $83.20  
  Purchase #4 $213.86   12.433%   $240.4492   $240.45   $240.45   $240.40  
  Purchase #5 $61.87   13.637%   $70.3072   $70.31   $70.30   $70.30  
  Purchase #6 $204.32   11.535%   $227.8883   $227.89   $227.90   $227.90  
  Purchase #7 $225.77   6.256%   $239.8942   $239.89   $239.90   $239.90  
  7 purchase totals = $1,122.59       $1,236.6500   $1,236.66   $1,236.65   $1,236.60