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 $115.48   13.404%   $130.9589   $130.96   $130.95   $131.00  
  Purchase #2 $30.88   5.295%   $32.5151   $32.52   $32.50   $32.50  
  Purchase #3 $119.61   5.767%   $126.5079   $126.51   $126.50   $126.50  
  Purchase #4 $207.64   4.642%   $217.2786   $217.28   $217.30   $217.30  
  Purchase #5 $67.69   11.663%   $75.5847   $75.58   $75.60   $75.60  
  Purchase #6 $144.95   5.759%   $153.2977   $153.30   $153.30   $153.30  
  Purchase #7 $183.74   6.436%   $195.5655   $195.57   $195.55   $195.60  
  7 purchase totals = $869.99       $931.7084   $931.72   $931.70   $931.80