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 $159.86   10.187%   $176.1449   $176.14   $176.15   $176.10  
  Purchase #2 $183.75   4.334%   $191.7137   $191.71   $191.70   $191.70  
  Purchase #3 $216.94   7.574%   $233.371   $233.37   $233.35   $233.40  
  Purchase #4 $229.81   11.790%   $256.9046   $256.90   $256.90   $256.90  
  Purchase #5 $56.69   4.569%   $59.2802   $59.28   $59.30   $59.30  
  Purchase #6 $199.29   12.393%   $223.988   $223.99   $224.00   $224.00  
  Purchase #7 $211.78   3.735%   $219.69   $219.69   $219.70   $219.70  
  7 purchase totals = $1,258.12       $1,361.0924   $1,361.08   $1,361.10   $1,361.10