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 $248.29   6.374%   $264.116   $264.12   $264.10   $264.10  
  Purchase #2 $234.81   8.684%   $255.2009   $255.20   $255.20   $255.20  
  Purchase #3 $94.96   6.450%   $101.0849   $101.08   $101.10   $101.10  
  Purchase #4 $235.84   5.595%   $249.0352   $249.04   $249.05   $249.00  
  Purchase #5 $201.90   9.288%   $220.6525   $220.65   $220.65   $220.70  
  Purchase #6 $195.28   4.143%   $203.3705   $203.37   $203.35   $203.40  
  Purchase #7 $64.63   3.206%   $66.702   $66.70   $66.70   $66.70  
  7 purchase totals = $1,275.71       $1,360.1620   $1,360.16   $1,360.15   $1,360.20