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 $223.89   10.439%   $247.2619   $247.26   $247.25   $247.30  
  Purchase #2 $24.42   6.247%   $25.9455   $25.95   $25.95   $25.90  
  Purchase #3 $178.76   5.360%   $188.3415   $188.34   $188.35   $188.30  
  Purchase #4 $74.81   9.658%   $82.0351   $82.04   $82.05   $82.00  
  Purchase #5 $197.53   6.642%   $210.6499   $210.65   $210.65   $210.60  
  Purchase #6 $187.94   5.483%   $198.2448   $198.24   $198.25   $198.20  
  Purchase #7 $52.29   11.151%   $58.1209   $58.12   $58.10   $58.10  
  7 purchase totals = $939.64       $1,010.5996   $1,010.60   $1,010.60   $1,010.40