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 $68.87   8.829%   $74.9505   $74.95   $74.95   $75.00  
  Purchase #2 $230.84   7.498%   $248.1484   $248.15   $248.15   $248.10  
  Purchase #3 $121.39   11.648%   $135.5295   $135.53   $135.55   $135.50  
  Purchase #4 $223.30   8.149%   $241.4967   $241.50   $241.50   $241.50  
  Purchase #5 $221.91   13.203%   $251.2088   $251.21   $251.20   $251.20  
  Purchase #6 $165.29   11.278%   $183.9314   $183.93   $183.95   $183.90  
  Purchase #7 $152.86   4.676%   $160.0077   $160.01   $160.00   $160.00  
  7 purchase totals = $1,184.46       $1,295.2730   $1,295.28   $1,295.30   $1,295.20