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 $69.46   12.523%   $78.1585   $78.16   $78.15   $78.20  
  Purchase #2 $180.39   11.627%   $201.3639   $201.36   $201.35   $201.40  
  Purchase #3 $244.71   8.682%   $265.9557   $265.96   $265.95   $266.00  
  Purchase #4 $127.48   6.169%   $135.3442   $135.34   $135.35   $135.30  
  Purchase #5 $192.98   8.495%   $209.3737   $209.37   $209.35   $209.40  
  Purchase #6 $179.70   7.499%   $193.1757   $193.18   $193.20   $193.20  
  Purchase #7 $63.87   5.298%   $67.2538   $67.25   $67.25   $67.30  
  7 purchase totals = $1,058.59       $1,150.6255   $1,150.62   $1,150.60   $1,150.80