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 $246.94   6.170%   $262.1762   $262.18   $262.20   $262.20  
  Purchase #2 $75.92   11.462%   $84.622   $84.62   $84.60   $84.60  
  Purchase #3 $53.93   3.771%   $55.9637   $55.96   $55.95   $56.00  
  Purchase #4 $49.96   6.372%   $53.1435   $53.14   $53.15   $53.10  
  Purchase #5 $216.85   13.681%   $246.5172   $246.52   $246.50   $246.50  
  Purchase #6 $101.90   6.196%   $108.2137   $108.21   $108.20   $108.20  
  Purchase #7 $171.34   12.856%   $193.3675   $193.37   $193.35   $193.40  
  7 purchase totals = $916.84       $1,004.0038   $1,004.00   $1,003.95   $1,004.00