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 $209.57   12.117%   $234.9636   $234.96   $234.95   $235.00  
  Purchase #2 $98.73   9.153%   $107.7668   $107.77   $107.75   $107.80  
  Purchase #3 $191.95   6.697%   $204.8049   $204.80   $204.80   $204.80  
  Purchase #4 $20.65   11.266%   $22.9764   $22.98   $23.00   $23.00  
  Purchase #5 $118.44   3.501%   $122.5866   $122.59   $122.60   $122.60  
  Purchase #6 $76.94   8.672%   $83.6122   $83.61   $83.60   $83.60  
  Purchase #7 $213.35   6.646%   $227.5292   $227.53   $227.55   $227.50  
  7 purchase totals = $929.63       $1,004.2397   $1,004.24   $1,004.25   $1,004.30