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 $124.48   8.159%   $134.6363   $134.64   $134.65   $134.60  
  Purchase #2 $249.25   6.787%   $266.1666   $266.17   $266.15   $266.20  
  Purchase #3 $12.58   13.761%   $14.3111   $14.31   $14.30   $14.30  
  Purchase #4 $215.73   6.667%   $230.1127   $230.11   $230.10   $230.10  
  Purchase #5 $47.50   9.434%   $51.9812   $51.98   $52.00   $52.00  
  Purchase #6 $161.86   13.165%   $183.1689   $183.17   $183.15   $183.20  
  Purchase #7 $179.73   6.116%   $190.7223   $190.72   $190.70   $190.70  
  7 purchase totals = $991.13       $1,071.0991   $1,071.10   $1,071.05   $1,071.10