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 $61.98   13.396%   $70.2828   $70.28   $70.30   $70.30  
  Purchase #2 $193.57   6.240%   $205.6488   $205.65   $205.65   $205.60  
  Purchase #3 $210.73   3.847%   $218.8368   $218.84   $218.85   $218.80  
  Purchase #4 $126.37   7.566%   $135.9312   $135.93   $135.95   $135.90  
  Purchase #5 $250.36   7.499%   $269.1345   $269.13   $269.15   $269.10  
  Purchase #6 $28.79   5.106%   $30.26   $30.26   $30.25   $30.30  
  Purchase #7 $168.62   3.648%   $174.7713   $174.77   $174.75   $174.80  
  7 purchase totals = $1,040.42       $1,104.8654   $1,104.86   $1,104.90   $1,104.80