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 $216.46   5.311%   $227.9562   $227.96   $227.95   $228.00  
  Purchase #2 $137.34   7.497%   $147.6364   $147.64   $147.65   $147.60  
  Purchase #3 $62.70   6.254%   $66.6213   $66.62   $66.60   $66.60  
  Purchase #4 $26.36   12.860%   $29.7499   $29.75   $29.75   $29.70  
  Purchase #5 $237.44   11.596%   $264.9735   $264.97   $264.95   $265.00  
  Purchase #6 $72.73   12.711%   $81.9747   $81.97   $81.95   $82.00  
  Purchase #7 $238.87   6.293%   $253.9021   $253.90   $253.90   $253.90  
  7 purchase totals = $991.90       $1,072.8141   $1,072.81   $1,072.75   $1,072.80