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 $61.35   7.226%   $65.7832   $65.78   $65.80   $65.80  
  Purchase #2 $185.65   6.157%   $197.0805   $197.08   $197.10   $197.10  
  Purchase #3 $128.90   4.830%   $135.1259   $135.13   $135.15   $135.10  
  Purchase #4 $20.68   9.406%   $22.6252   $22.63   $22.65   $22.60  
  Purchase #5 $81.27   9.215%   $88.759   $88.76   $88.75   $88.80  
  Purchase #6 $205.91   4.557%   $215.2933   $215.29   $215.30   $215.30  
  Purchase #7 $22.33   8.670%   $24.266   $24.27   $24.25   $24.30  
  7 purchase totals = $706.09       $748.9331   $748.94   $749.00   $749.00