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 $244.41   11.453%   $272.4023   $272.40   $272.40   $272.40  
  Purchase #2 $210.79   7.364%   $226.3126   $226.31   $226.30   $226.30  
  Purchase #3 $178.44   3.142%   $184.0466   $184.05   $184.05   $184.00  
  Purchase #4 $65.77   12.176%   $73.7782   $73.78   $73.80   $73.80  
  Purchase #5 $150.51   6.387%   $160.1231   $160.12   $160.10   $160.10  
  Purchase #6 $239.73   6.678%   $255.7392   $255.74   $255.75   $255.70  
  Purchase #7 $116.80   4.726%   $122.32   $122.32   $122.30   $122.30  
  7 purchase totals = $1,206.45       $1,294.7220   $1,294.72   $1,294.70   $1,294.60