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 $241.28   12.619%   $271.7271   $271.73   $271.75   $271.70  
  Purchase #2 $103.76   5.411%   $109.3745   $109.37   $109.35   $109.40  
  Purchase #3 $97.57   5.309%   $102.75   $102.75   $102.75   $102.80  
  Purchase #4 $39.53   4.759%   $41.4112   $41.41   $41.40   $41.40  
  Purchase #5 $194.66   9.532%   $213.215   $213.22   $213.20   $213.20  
  Purchase #6 $169.25   3.750%   $175.5969   $175.60   $175.60   $175.60  
  Purchase #7 $187.61   10.612%   $207.5192   $207.52   $207.50   $207.50  
  7 purchase totals = $1,033.66       $1,121.5939   $1,121.60   $1,121.55   $1,121.60