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 $189.35   8.808%   $206.0279   $206.03   $206.05   $206.00  
  Purchase #2 $239.47   11.230%   $266.3625   $266.36   $266.35   $266.40  
  Purchase #3 $26.67   3.621%   $27.6357   $27.64   $27.65   $27.60  
  Purchase #4 $36.68   10.539%   $40.5457   $40.55   $40.55   $40.50  
  Purchase #5 $120.65   8.589%   $131.0126   $131.01   $131.00   $131.00  
  Purchase #6 $167.89   6.829%   $179.3552   $179.36   $179.35   $179.40  
  Purchase #7 $135.79   5.723%   $143.5613   $143.56   $143.55   $143.60  
  7 purchase totals = $916.50       $994.5009   $994.51   $994.50   $994.50