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 $66.82   3.321%   $69.0391   $69.04   $69.05   $69.00  
  Purchase #2 $136.72   6.250%   $145.265   $145.27   $145.25   $145.30  
  Purchase #3 $67.51   11.647%   $75.3729   $75.37   $75.35   $75.40  
  Purchase #4 $240.93   4.103%   $250.8154   $250.82   $250.80   $250.80  
  Purchase #5 $180.95   5.470%   $190.848   $190.85   $190.85   $190.80  
  Purchase #6 $95.71   11.586%   $106.799   $106.80   $106.80   $106.80  
  Purchase #7 $122.64   8.446%   $132.9982   $133.00   $133.00   $133.00  
  7 purchase totals = $911.28       $971.1376   $971.15   $971.10   $971.10