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 $22.87   12.572%   $25.7452   $25.75   $25.75   $25.70  
  Purchase #2 $175.33   12.330%   $196.9482   $196.95   $196.95   $196.90  
  Purchase #3 $177.57   7.417%   $190.7404   $190.74   $190.75   $190.70  
  Purchase #4 $24.80   10.812%   $27.4814   $27.48   $27.50   $27.50  
  Purchase #5 $192.51   10.111%   $211.9747   $211.97   $211.95   $212.00  
  Purchase #6 $103.56   6.622%   $110.4177   $110.42   $110.40   $110.40  
  Purchase #7 $177.60   8.403%   $192.5237   $192.52   $192.50   $192.50  
  7 purchase totals = $874.24       $955.8313   $955.83   $955.80   $955.70