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 $83.53   5.467%   $88.0966   $88.10   $88.10   $88.10  
  Purchase #2 $163.89   12.796%   $184.8614   $184.86   $184.85   $184.90  
  Purchase #3 $14.28   10.553%   $15.787   $15.79   $15.80   $15.80  
  Purchase #4 $41.97   3.402%   $43.3978   $43.40   $43.40   $43.40  
  Purchase #5 $60.41   10.190%   $66.5658   $66.57   $66.55   $66.60  
  Purchase #6 $72.68   5.320%   $76.5466   $76.55   $76.55   $76.50  
  Purchase #7 $245.51   8.251%   $265.767   $265.77   $265.75   $265.80  
  7 purchase totals = $682.27       $741.0222   $741.04   $741.00   $741.10