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 $172.89   7.441%   $185.7547   $185.75   $185.75   $185.80  
  Purchase #2 $69.61   3.292%   $71.9016   $71.90   $71.90   $71.90  
  Purchase #3 $144.62   10.251%   $159.445   $159.45   $159.45   $159.40  
  Purchase #4 $233.57   7.514%   $251.1204   $251.12   $251.10   $251.10  
  Purchase #5 $94.43   4.416%   $98.6   $98.60   $98.60   $98.60  
  Purchase #6 $217.90   11.689%   $243.3703   $243.37   $243.35   $243.40  
  Purchase #7 $192.76   12.255%   $216.3827   $216.38   $216.40   $216.40  
  7 purchase totals = $1,125.78       $1,226.5747   $1,226.57   $1,226.55   $1,226.60