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 $23.70   13.675%   $26.941   $26.94   $26.95   $26.90  
  Purchase #2 $234.41   5.199%   $246.597   $246.60   $246.60   $246.60  
  Purchase #3 $200.37   13.481%   $227.3819   $227.38   $227.40   $227.40  
  Purchase #4 $94.55   10.136%   $104.1336   $104.13   $104.15   $104.10  
  Purchase #5 $222.39   3.842%   $230.9342   $230.93   $230.95   $230.90  
  Purchase #6 $166.72   6.287%   $177.2017   $177.20   $177.20   $177.20  
  Purchase #7 $210.57   3.678%   $218.3148   $218.31   $218.30   $218.30  
  7 purchase totals = $1,152.71       $1,231.5042   $1,231.49   $1,231.55   $1,231.40