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 $123.86   8.344%   $134.1949   $134.19   $134.20   $134.20  
  Purchase #2 $12.65   9.647%   $13.8703   $13.87   $13.85   $13.90  
  Purchase #3 $246.33   3.470%   $254.8777   $254.88   $254.90   $254.90  
  Purchase #4 $125.88   6.681%   $134.29   $134.29   $134.30   $134.30  
  Purchase #5 $61.75   4.738%   $64.6757   $64.68   $64.70   $64.70  
  Purchase #6 $186.39   10.620%   $206.1846   $206.18   $206.20   $206.20  
  Purchase #7 $190.29   8.826%   $207.085   $207.09   $207.10   $207.10  
  7 purchase totals = $947.15       $1,015.1782   $1,015.18   $1,015.25   $1,015.30