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 $118.50   13.249%   $134.2001   $134.20   $134.20   $134.20  
  Purchase #2 $27.65   8.692%   $30.0533   $30.05   $30.05   $30.10  
  Purchase #3 $75.61   5.701%   $79.9205   $79.92   $79.90   $79.90  
  Purchase #4 $238.84   13.766%   $271.7187   $271.72   $271.70   $271.70  
  Purchase #5 $194.25   5.855%   $205.6233   $205.62   $205.60   $205.60  
  Purchase #6 $82.54   6.360%   $87.7895   $87.79   $87.80   $87.80  
  Purchase #7 $172.97   7.823%   $186.5014   $186.50   $186.50   $186.50  
  7 purchase totals = $910.36       $995.8068   $995.80   $995.75   $995.80