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 $107.84   9.444%   $118.0244   $118.02   $118.00   $118.00  
  Purchase #2 $60.95   6.196%   $64.7265   $64.73   $64.75   $64.70  
  Purchase #3 $63.83   11.274%   $71.0262   $71.03   $71.05   $71.00  
  Purchase #4 $219.72   6.437%   $233.8634   $233.86   $233.85   $233.90  
  Purchase #5 $213.40   12.311%   $239.6717   $239.67   $239.65   $239.70  
  Purchase #6 $196.76   10.247%   $216.922   $216.92   $216.90   $216.90  
  Purchase #7 $141.58   6.709%   $151.0786   $151.08   $151.10   $151.10  
  7 purchase totals = $1,004.08       $1,095.3128   $1,095.31   $1,095.30   $1,095.30