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 $126.95   6.297%   $134.944   $134.94   $134.95   $134.90  
  Purchase #2 $220.26   6.172%   $233.8544   $233.85   $233.85   $233.90  
  Purchase #3 $241.67   9.647%   $264.9839   $264.98   $265.00   $265.00  
  Purchase #4 $146.42   12.165%   $164.232   $164.23   $164.25   $164.20  
  Purchase #5 $185.89   7.247%   $199.3614   $199.36   $199.35   $199.40  
  Purchase #6 $76.33   12.102%   $85.5675   $85.57   $85.55   $85.60  
  Purchase #7 $8.94   6.565%   $9.5269   $9.53   $9.55   $9.50  
  7 purchase totals = $1,006.46       $1,092.4701   $1,092.46   $1,092.50   $1,092.50