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 $193.82   6.615%   $206.6412   $206.64   $206.65   $206.60  
  Purchase #2 $184.67   6.874%   $197.3642   $197.36   $197.35   $197.40  
  Purchase #3 $164.68   7.482%   $177.0014   $177.00   $177.00   $177.00  
  Purchase #4 $157.33   10.852%   $174.4035   $174.40   $174.40   $174.40  
  Purchase #5 $211.65   6.330%   $225.0474   $225.05   $225.05   $225.00  
  Purchase #6 $78.27   4.660%   $81.9174   $81.92   $81.90   $81.90  
  Purchase #7 $184.83   5.280%   $194.589   $194.59   $194.60   $194.60  
  7 purchase totals = $1,175.25       $1,256.9641   $1,256.96   $1,256.95   $1,256.90