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 $77.53   6.681%   $82.7098   $82.71   $82.70   $82.70  
  Purchase #2 $161.32   13.228%   $182.6594   $182.66   $182.65   $182.70  
  Purchase #3 $67.91   9.818%   $74.5774   $74.58   $74.60   $74.60  
  Purchase #4 $24.97   11.746%   $27.903   $27.90   $27.90   $27.90  
  Purchase #5 $230.27   9.346%   $251.791   $251.79   $251.80   $251.80  
  Purchase #6 $237.28   9.761%   $260.4409   $260.44   $260.45   $260.40  
  Purchase #7 $180.59   11.396%   $201.17   $201.17   $201.15   $201.20  
  7 purchase totals = $979.87       $1,081.2515   $1,081.25   $1,081.25   $1,081.30