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 $44.72   11.831%   $50.0108   $50.01   $50.00   $50.00  
  Purchase #2 $181.73   8.353%   $196.9099   $196.91   $196.90   $196.90  
  Purchase #3 $191.80   10.216%   $211.3943   $211.39   $211.40   $211.40  
  Purchase #4 $194.32   5.722%   $205.439   $205.44   $205.45   $205.40  
  Purchase #5 $99.66   7.439%   $107.0737   $107.07   $107.05   $107.10  
  Purchase #6 $231.62   6.359%   $246.3487   $246.35   $246.35   $246.30  
  Purchase #7 $5.51   7.423%   $5.919   $5.92   $5.90   $5.90  
  7 purchase totals = $949.36       $1,023.0954   $1,023.09   $1,023.05   $1,023.00