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 $123.37   6.132%   $130.935   $130.94   $130.95   $130.90  
  Purchase #2 $239.64   10.143%   $263.9467   $263.95   $263.95   $263.90  
  Purchase #3 $59.69   9.577%   $65.4065   $65.41   $65.40   $65.40  
  Purchase #4 $204.82   11.493%   $228.36   $228.36   $228.35   $228.40  
  Purchase #5 $212.31   5.255%   $223.4669   $223.47   $223.45   $223.50  
  Purchase #6 $132.98   9.483%   $145.5905   $145.59   $145.60   $145.60  
  Purchase #7 $196.63   8.112%   $212.5806   $212.58   $212.60   $212.60  
  7 purchase totals = $1,169.44       $1,270.2862   $1,270.30   $1,270.30   $1,270.30