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 $183.79   10.576%   $203.2276   $203.23   $203.25   $203.20  
  Purchase #2 $136.95   8.469%   $148.5483   $148.55   $148.55   $148.50  
  Purchase #3 $51.36   7.406%   $55.1637   $55.16   $55.15   $55.20  
  Purchase #4 $151.61   7.357%   $162.7639   $162.76   $162.75   $162.80  
  Purchase #5 $165.54   6.284%   $175.9425   $175.94   $175.95   $175.90  
  Purchase #6 $182.80   10.231%   $201.5023   $201.50   $201.50   $201.50  
  Purchase #7 $228.83   7.871%   $246.8412   $246.84   $246.85   $246.80  
  7 purchase totals = $1,100.88       $1,193.9895   $1,193.98   $1,194.00   $1,193.90