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 $204.49   5.618%   $215.9782   $215.98   $216.00   $216.00  
  Purchase #2 $145.70   13.367%   $165.1757   $165.18   $165.20   $165.20  
  Purchase #3 $25.80   9.696%   $28.3016   $28.30   $28.30   $28.30  
  Purchase #4 $187.95   9.626%   $206.0421   $206.04   $206.05   $206.00  
  Purchase #5 $89.37   3.688%   $92.666   $92.67   $92.65   $92.70  
  Purchase #6 $120.69   11.782%   $134.9097   $134.91   $134.90   $134.90  
  Purchase #7 $171.64   8.674%   $186.5281   $186.53   $186.55   $186.50  
  7 purchase totals = $945.64       $1,029.6014   $1,029.61   $1,029.65   $1,029.60