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 $174.74   11.513%   $194.8578   $194.86   $194.85   $194.90  
  Purchase #2 $222.53   13.398%   $252.3446   $252.34   $252.35   $252.30  
  Purchase #3 $244.82   6.208%   $260.0184   $260.02   $260.00   $260.00  
  Purchase #4 $56.38   11.274%   $62.7363   $62.74   $62.75   $62.70  
  Purchase #5 $147.90   7.746%   $159.3563   $159.36   $159.35   $159.40  
  Purchase #6 $194.94   6.499%   $207.6092   $207.61   $207.60   $207.60  
  Purchase #7 $58.65   3.523%   $60.7162   $60.72   $60.70   $60.70  
  7 purchase totals = $1,099.96       $1,197.6388   $1,197.65   $1,197.60   $1,197.60