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 $86.78   8.118%   $93.8248   $93.82   $93.80   $93.80  
  Purchase #2 $148.53   8.611%   $161.3199   $161.32   $161.30   $161.30  
  Purchase #3 $207.92   13.371%   $235.721   $235.72   $235.70   $235.70  
  Purchase #4 $168.98   12.397%   $189.9285   $189.93   $189.95   $189.90  
  Purchase #5 $74.33   10.151%   $81.8752   $81.88   $81.90   $81.90  
  Purchase #6 $33.61   11.749%   $37.5588   $37.56   $37.55   $37.60  
  Purchase #7 $208.80   10.311%   $230.3294   $230.33   $230.35   $230.30  
  7 purchase totals = $928.95       $1,030.5576   $1,030.56   $1,030.55   $1,030.50