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 $62.35   13.110%   $70.5241   $70.52   $70.50   $70.50  
  Purchase #2 $106.76   10.718%   $118.2025   $118.20   $118.20   $118.20  
  Purchase #3 $101.82   5.170%   $107.0841   $107.08   $107.10   $107.10  
  Purchase #4 $129.86   5.555%   $137.0737   $137.07   $137.05   $137.10  
  Purchase #5 $61.67   13.607%   $70.0614   $70.06   $70.05   $70.10  
  Purchase #6 $158.74   3.799%   $164.7705   $164.77   $164.75   $164.80  
  Purchase #7 $24.35   9.411%   $26.6416   $26.64   $26.65   $26.60  
  7 purchase totals = $645.55       $694.3579   $694.34   $694.30   $694.40