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 $242.69   4.321%   $253.1766   $253.18   $253.20   $253.20  
  Purchase #2 $94.56   9.191%   $103.251   $103.25   $103.25   $103.30  
  Purchase #3 $186.55   12.405%   $209.6915   $209.69   $209.70   $209.70  
  Purchase #4 $135.74   4.183%   $141.418   $141.42   $141.40   $141.40  
  Purchase #5 $218.45   7.122%   $234.008   $234.01   $234.00   $234.00  
  Purchase #6 $187.55   11.373%   $208.8801   $208.88   $208.90   $208.90  
  Purchase #7 $149.84   9.133%   $163.5249   $163.52   $163.50   $163.50  
  7 purchase totals = $1,215.38       $1,313.9501   $1,313.95   $1,313.95   $1,314.00