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 $219.39   13.124%   $248.1827   $248.18   $248.20   $248.20  
  Purchase #2 $94.29   11.771%   $105.3889   $105.39   $105.40   $105.40  
  Purchase #3 $194.37   11.480%   $216.6837   $216.68   $216.70   $216.70  
  Purchase #4 $86.99   12.495%   $97.8594   $97.86   $97.85   $97.90  
  Purchase #5 $234.45   4.747%   $245.5793   $245.58   $245.60   $245.60  
  Purchase #6 $7.71   9.284%   $8.4258   $8.43   $8.45   $8.40  
  Purchase #7 $130.48   13.423%   $147.9943   $147.99   $148.00   $148.00  
  7 purchase totals = $967.68       $1,070.1141   $1,070.11   $1,070.20   $1,070.20