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 $249.43   9.784%   $273.8342   $273.83   $273.85   $273.80  
  Purchase #2 $105.27   13.588%   $119.5741   $119.57   $119.55   $119.60  
  Purchase #3 $229.52   8.782%   $249.6764   $249.68   $249.70   $249.70  
  Purchase #4 $68.32   8.163%   $73.897   $73.90   $73.90   $73.90  
  Purchase #5 $94.75   5.264%   $99.7376   $99.74   $99.75   $99.70  
  Purchase #6 $163.27   7.317%   $175.2165   $175.22   $175.20   $175.20  
  Purchase #7 $74.72   3.220%   $77.126   $77.13   $77.15   $77.10  
  7 purchase totals = $985.28       $1,069.0618   $1,069.07   $1,069.10   $1,069.00