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 $233.49   12.534%   $262.7556   $262.76   $262.75   $262.80  
  Purchase #2 $152.32   7.669%   $164.0014   $164.00   $164.00   $164.00  
  Purchase #3 $62.89   7.372%   $67.5263   $67.53   $67.55   $67.50  
  Purchase #4 $153.42   13.310%   $173.8402   $173.84   $173.85   $173.80  
  Purchase #5 $109.87   7.357%   $117.9531   $117.95   $117.95   $118.00  
  Purchase #6 $124.33   6.759%   $132.7335   $132.73   $132.75   $132.70  
  Purchase #7 $125.56   8.418%   $136.1296   $136.13   $136.15   $136.10  
  7 purchase totals = $961.88       $1,054.9397   $1,054.94   $1,055.00   $1,054.90