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 $218.56   10.519%   $241.5503   $241.55   $241.55   $241.60  
  Purchase #2 $168.98   11.102%   $187.7402   $187.74   $187.75   $187.70  
  Purchase #3 $249.99   7.685%   $269.2017   $269.20   $269.20   $269.20  
  Purchase #4 $17.65   13.605%   $20.0513   $20.05   $20.05   $20.10  
  Purchase #5 $155.87   10.582%   $172.3642   $172.36   $172.35   $172.40  
  Purchase #6 $60.66   12.663%   $68.3414   $68.34   $68.35   $68.30  
  Purchase #7 $194.76   3.343%   $201.2708   $201.27   $201.25   $201.30  
  7 purchase totals = $1,066.47       $1,160.5199   $1,160.51   $1,160.50   $1,160.60