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 $111.91   12.835%   $126.2736   $126.27   $126.25   $126.30  
  Purchase #2 $230.84   8.709%   $250.9439   $250.94   $250.95   $250.90  
  Purchase #3 $111.29   9.757%   $122.1486   $122.15   $122.15   $122.10  
  Purchase #4 $94.87   4.574%   $99.2094   $99.21   $99.20   $99.20  
  Purchase #5 $167.98   9.448%   $183.8508   $183.85   $183.85   $183.90  
  Purchase #6 $171.30   11.842%   $191.5853   $191.59   $191.60   $191.60  
  Purchase #7 $98.64   6.124%   $104.6807   $104.68   $104.70   $104.70  
  7 purchase totals = $986.83       $1,078.6923   $1,078.69   $1,078.70   $1,078.70