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 $60.88   9.560%   $66.7001   $66.70   $66.70   $66.70  
  Purchase #2 $233.31   9.412%   $255.2691   $255.27   $255.25   $255.30  
  Purchase #3 $194.90   4.439%   $203.5516   $203.55   $203.55   $203.60  
  Purchase #4 $167.85   6.598%   $178.9247   $178.92   $178.90   $178.90  
  Purchase #5 $44.80   8.621%   $48.6622   $48.66   $48.65   $48.70  
  Purchase #6 $61.60   8.477%   $66.8218   $66.82   $66.80   $66.80  
  Purchase #7 $168.92   12.367%   $189.8103   $189.81   $189.80   $189.80  
  7 purchase totals = $932.26       $1,009.7398   $1,009.73   $1,009.65   $1,009.80