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 $192.65   3.134%   $198.6877   $198.69   $198.70   $198.70  
  Purchase #2 $230.38   4.861%   $241.5788   $241.58   $241.60   $241.60  
  Purchase #3 $154.41   12.139%   $173.1538   $173.15   $173.15   $173.20  
  Purchase #4 $215.76   7.447%   $231.8276   $231.83   $231.85   $231.80  
  Purchase #5 $232.46   9.559%   $254.6809   $254.68   $254.70   $254.70  
  Purchase #6 $46.36   11.551%   $51.715   $51.72   $51.70   $51.70  
  Purchase #7 $99.26   5.428%   $104.6478   $104.65   $104.65   $104.60  
  7 purchase totals = $1,171.28       $1,256.2916   $1,256.30   $1,256.35   $1,256.30