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 $106.34   12.605%   $119.7442   $119.74   $119.75   $119.70  
  Purchase #2 $10.91   11.752%   $12.1921   $12.19   $12.20   $12.20  
  Purchase #3 $105.72   7.291%   $113.428   $113.43   $113.45   $113.40  
  Purchase #4 $241.25   7.504%   $259.3534   $259.35   $259.35   $259.40  
  Purchase #5 $249.76   7.347%   $268.1099   $268.11   $268.10   $268.10  
  Purchase #6 $167.29   6.328%   $177.8761   $177.88   $177.90   $177.90  
  Purchase #7 $131.66   7.789%   $141.915   $141.92   $141.90   $141.90  
  7 purchase totals = $1,012.93       $1,092.6187   $1,092.62   $1,092.65   $1,092.60