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 $86.71   13.366%   $98.2997   $98.30   $98.30   $98.30  
  Purchase #2 $184.60   10.199%   $203.4274   $203.43   $203.45   $203.40  
  Purchase #3 $208.78   6.861%   $223.1044   $223.10   $223.10   $223.10  
  Purchase #4 $223.51   4.470%   $233.5009   $233.50   $233.50   $233.50  
  Purchase #5 $130.95   12.173%   $146.8905   $146.89   $146.90   $146.90  
  Purchase #6 $118.68   6.573%   $126.4808   $126.48   $126.50   $126.50  
  Purchase #7 $238.56   5.784%   $252.3583   $252.36   $252.35   $252.40  
  7 purchase totals = $1,191.79       $1,284.0620   $1,284.06   $1,284.10   $1,284.10