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 $63.25   7.577%   $68.0425   $68.04   $68.05   $68.00  
  Purchase #2 $242.68   8.662%   $263.7009   $263.70   $263.70   $263.70  
  Purchase #3 $223.30   11.210%   $248.3319   $248.33   $248.35   $248.30  
  Purchase #4 $199.98   9.672%   $219.3221   $219.32   $219.30   $219.30  
  Purchase #5 $179.57   13.578%   $203.952   $203.95   $203.95   $204.00  
  Purchase #6 $150.98   4.342%   $157.5356   $157.54   $157.55   $157.50  
  Purchase #7 $102.83   4.764%   $107.7288   $107.73   $107.75   $107.70  
  7 purchase totals = $1,162.59       $1,268.6138   $1,268.61   $1,268.65   $1,268.50