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 $26.85   10.765%   $29.7404   $29.74   $29.75   $29.70  
  Purchase #2 $249.42   11.406%   $277.8688   $277.87   $277.85   $277.90  
  Purchase #3 $118.42   10.128%   $130.4136   $130.41   $130.40   $130.40  
  Purchase #4 $216.52   9.806%   $237.752   $237.75   $237.75   $237.80  
  Purchase #5 $123.37   6.572%   $131.4779   $131.48   $131.50   $131.50  
  Purchase #6 $33.79   10.368%   $37.2933   $37.29   $37.30   $37.30  
  Purchase #7 $162.57   4.411%   $169.741   $169.74   $169.75   $169.70  
  7 purchase totals = $930.94       $1,014.2870   $1,014.28   $1,014.30   $1,014.30