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 $68.59   7.662%   $73.8454   $73.85   $73.85   $73.80  
  Purchase #2 $224.26   13.368%   $254.2391   $254.24   $254.25   $254.20  
  Purchase #3 $165.70   8.461%   $179.7199   $179.72   $179.70   $179.70  
  Purchase #4 $209.95   11.286%   $233.645   $233.65   $233.65   $233.60  
  Purchase #5 $56.42   7.629%   $60.7243   $60.72   $60.70   $60.70  
  Purchase #6 $42.57   11.268%   $47.3668   $47.37   $47.35   $47.40  
  Purchase #7 $173.61   13.285%   $196.6741   $196.67   $196.65   $196.70  
  7 purchase totals = $941.10       $1,046.2146   $1,046.22   $1,046.15   $1,046.10