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 $217.41   10.459%   $240.1489   $240.15   $240.15   $240.10  
  Purchase #2 $68.32   9.431%   $74.7633   $74.76   $74.75   $74.80  
  Purchase #3 $107.71   12.249%   $120.9034   $120.90   $120.90   $120.90  
  Purchase #4 $194.92   11.450%   $217.2383   $217.24   $217.25   $217.20  
  Purchase #5 $228.44   5.751%   $241.5776   $241.58   $241.60   $241.60  
  Purchase #6 $157.43   6.524%   $167.7007   $167.70   $167.70   $167.70  
  Purchase #7 $148.34   12.697%   $167.1747   $167.17   $167.15   $167.20  
  7 purchase totals = $1,122.57       $1,229.5069   $1,229.50   $1,229.50   $1,229.50