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 $95.56   5.332%   $100.6553   $100.66   $100.65   $100.70  
  Purchase #2 $177.78   12.846%   $200.6176   $200.62   $200.60   $200.60  
  Purchase #3 $226.78   3.857%   $235.5269   $235.53   $235.55   $235.50  
  Purchase #4 $218.75   12.617%   $246.3497   $246.35   $246.35   $246.30  
  Purchase #5 $51.85   11.838%   $57.988   $57.99   $58.00   $58.00  
  Purchase #6 $63.67   11.298%   $70.8634   $70.86   $70.85   $70.90  
  Purchase #7 $117.79   9.285%   $128.7268   $128.73   $128.75   $128.70  
  7 purchase totals = $952.18       $1,040.7277   $1,040.74   $1,040.75   $1,040.70