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 $183.51   12.749%   $206.9057   $206.91   $206.90   $206.90  
  Purchase #2 $239.85   5.475%   $252.9818   $252.98   $253.00   $253.00  
  Purchase #3 $83.99   4.772%   $87.998   $88.00   $88.00   $88.00  
  Purchase #4 $39.67   13.236%   $44.9207   $44.92   $44.90   $44.90  
  Purchase #5 $61.82   4.447%   $64.5691   $64.57   $64.55   $64.60  
  Purchase #6 $155.87   4.432%   $162.7782   $162.78   $162.80   $162.80  
  Purchase #7 $193.43   3.261%   $199.7378   $199.74   $199.75   $199.70  
  7 purchase totals = $958.14       $1,019.8913   $1,019.90   $1,019.90   $1,019.90