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 $145.58   5.371%   $153.3991   $153.40   $153.40   $153.40  
  Purchase #2 $215.79   11.852%   $241.3654   $241.37   $241.35   $241.40  
  Purchase #3 $148.69   7.358%   $159.6306   $159.63   $159.65   $159.60  
  Purchase #4 $23.65   11.232%   $26.3064   $26.31   $26.30   $26.30  
  Purchase #5 $97.67   7.277%   $104.7774   $104.78   $104.80   $104.80  
  Purchase #6 $53.29   3.548%   $55.1807   $55.18   $55.20   $55.20  
  Purchase #7 $241.55   9.509%   $264.519   $264.52   $264.50   $264.50  
  7 purchase totals = $926.22       $1,005.1786   $1,005.19   $1,005.20   $1,005.20