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 $166.75   8.721%   $181.2923   $181.29   $181.30   $181.30  
  Purchase #2 $183.68   10.318%   $202.6321   $202.63   $202.65   $202.60  
  Purchase #3 $225.59   8.251%   $244.2034   $244.20   $244.20   $244.20  
  Purchase #4 $224.86   12.781%   $253.5994   $253.60   $253.60   $253.60  
  Purchase #5 $57.52   12.642%   $64.7917   $64.79   $64.80   $64.80  
  Purchase #6 $103.78   10.728%   $114.9135   $114.91   $114.90   $114.90  
  Purchase #7 $109.57   5.161%   $115.2249   $115.22   $115.20   $115.20  
  7 purchase totals = $1,071.75       $1,176.6573   $1,176.64   $1,176.65   $1,176.60