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 $107.25   11.582%   $119.6717   $119.67   $119.65   $119.70  
  Purchase #2 $250.53   7.106%   $268.3327   $268.33   $268.35   $268.30  
  Purchase #3 $212.77   8.625%   $231.1214   $231.12   $231.10   $231.10  
  Purchase #4 $52.37   12.403%   $58.8655   $58.87   $58.85   $58.90  
  Purchase #5 $179.35   12.295%   $201.4011   $201.40   $201.40   $201.40  
  Purchase #6 $118.61   7.286%   $127.2519   $127.25   $127.25   $127.30  
  Purchase #7 $63.28   4.736%   $66.2769   $66.28   $66.30   $66.30  
  7 purchase totals = $984.16       $1,072.9212   $1,072.92   $1,072.90   $1,073.00