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 $209.45   7.262%   $224.6603   $224.66   $224.65   $224.70  
  Purchase #2 $112.38   8.196%   $121.5907   $121.59   $121.60   $121.60  
  Purchase #3 $108.58   13.123%   $122.829   $122.83   $122.85   $122.80  
  Purchase #4 $241.41   7.646%   $259.8682   $259.87   $259.85   $259.90  
  Purchase #5 $206.82   11.668%   $230.9518   $230.95   $230.95   $231.00  
  Purchase #6 $170.90   7.348%   $183.4577   $183.46   $183.45   $183.50  
  Purchase #7 $60.48   3.466%   $62.5762   $62.58   $62.60   $62.60  
  7 purchase totals = $1,110.02       $1,205.9339   $1,205.94   $1,205.95   $1,206.10