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 $216.66   11.652%   $241.9052   $241.91   $241.90   $241.90  
  Purchase #2 $93.75   4.348%   $97.8263   $97.83   $97.85   $97.80  
  Purchase #3 $238.66   7.807%   $257.2922   $257.29   $257.30   $257.30  
  Purchase #4 $17.31   10.363%   $19.1038   $19.10   $19.10   $19.10  
  Purchase #5 $21.25   3.525%   $21.9991   $22.00   $22.00   $22.00  
  Purchase #6 $159.72   5.801%   $168.9854   $168.99   $169.00   $169.00  
  Purchase #7 $202.65   5.771%   $214.3449   $214.34   $214.35   $214.30  
  7 purchase totals = $950.00       $1,021.4569   $1,021.46   $1,021.50   $1,021.40