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 $121.40   12.449%   $136.5131   $136.51   $136.50   $136.50  
  Purchase #2 $158.96   5.445%   $167.6154   $167.62   $167.60   $167.60  
  Purchase #3 $35.51   3.144%   $36.6264   $36.63   $36.65   $36.60  
  Purchase #4 $94.46   3.740%   $97.9928   $97.99   $98.00   $98.00  
  Purchase #5 $213.62   8.385%   $231.532   $231.53   $231.55   $231.50  
  Purchase #6 $103.33   9.565%   $113.2135   $113.21   $113.20   $113.20  
  Purchase #7 $216.94   6.470%   $230.976   $230.98   $231.00   $231.00  
  7 purchase totals = $944.22       $1,014.4692   $1,014.47   $1,014.50   $1,014.40