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 $244.63   13.306%   $277.1805   $277.18   $277.20   $277.20  
  Purchase #2 $250.47   6.435%   $266.5877   $266.59   $266.60   $266.60  
  Purchase #3 $34.52   5.270%   $36.3392   $36.34   $36.35   $36.30  
  Purchase #4 $59.87   7.503%   $64.362   $64.36   $64.35   $64.40  
  Purchase #5 $100.91   13.527%   $114.5601   $114.56   $114.55   $114.60  
  Purchase #6 $119.55   7.289%   $128.264   $128.26   $128.25   $128.30  
  Purchase #7 $249.73   13.647%   $283.8107   $283.81   $283.80   $283.80  
  7 purchase totals = $1,059.68       $1,171.1042   $1,171.10   $1,171.10   $1,171.20