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 $144.80   9.780%   $158.9614   $158.96   $158.95   $159.00  
  Purchase #2 $249.90   10.671%   $276.5668   $276.57   $276.55   $276.60  
  Purchase #3 $48.36   10.564%   $53.4688   $53.47   $53.45   $53.50  
  Purchase #4 $91.56   12.203%   $102.7331   $102.73   $102.75   $102.70  
  Purchase #5 $197.94   9.829%   $217.3955   $217.40   $217.40   $217.40  
  Purchase #6 $231.81   6.363%   $246.5601   $246.56   $246.55   $246.60  
  Purchase #7 $162.92   3.379%   $168.4251   $168.43   $168.45   $168.40  
  7 purchase totals = $1,127.29       $1,224.1108   $1,224.12   $1,224.10   $1,224.20