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 $83.99   10.205%   $92.5612   $92.56   $92.55   $92.60  
  Purchase #2 $31.59   9.488%   $34.5873   $34.59   $34.60   $34.60  
  Purchase #3 $87.31   8.816%   $95.0072   $95.01   $95.00   $95.00  
  Purchase #4 $53.82   5.672%   $56.8727   $56.87   $56.85   $56.90  
  Purchase #5 $42.51   5.326%   $44.7741   $44.77   $44.75   $44.80  
  Purchase #6 $235.55   5.836%   $249.2967   $249.30   $249.30   $249.30  
  Purchase #7 $11.90   12.288%   $13.3623   $13.36   $13.35   $13.40  
  7 purchase totals = $546.67       $586.4615   $586.46   $586.40   $586.60