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 $183.67   8.132%   $198.606   $198.61   $198.60   $198.60  
  Purchase #2 $119.94   13.547%   $136.1883   $136.19   $136.20   $136.20  
  Purchase #3 $217.34   4.389%   $226.8791   $226.88   $226.90   $226.90  
  Purchase #4 $42.32   8.580%   $45.9511   $45.95   $45.95   $46.00  
  Purchase #5 $162.27   10.406%   $179.1558   $179.16   $179.15   $179.20  
  Purchase #6 $108.88   3.660%   $112.865   $112.87   $112.85   $112.90  
  Purchase #7 $155.51   9.694%   $170.5851   $170.59   $170.60   $170.60  
  7 purchase totals = $989.93       $1,070.2304   $1,070.25   $1,070.25   $1,070.40