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 $235.48   7.779%   $253.798   $253.80   $253.80   $253.80  
  Purchase #2 $51.45   5.569%   $54.3153   $54.32   $54.30   $54.30  
  Purchase #3 $152.72   4.679%   $159.8658   $159.87   $159.85   $159.90  
  Purchase #4 $88.79   8.790%   $96.5946   $96.59   $96.60   $96.60  
  Purchase #5 $166.64   13.687%   $189.448   $189.45   $189.45   $189.40  
  Purchase #6 $147.84   4.807%   $154.9467   $154.95   $154.95   $154.90  
  Purchase #7 $13.94   12.729%   $15.7144   $15.71   $15.70   $15.70  
  7 purchase totals = $856.86       $924.6828   $924.69   $924.65   $924.60