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 $183.99   6.822%   $196.5418   $196.54   $196.55   $196.50  
  Purchase #2 $158.92   11.785%   $177.6487   $177.65   $177.65   $177.60  
  Purchase #3 $164.41   9.647%   $180.2706   $180.27   $180.25   $180.30  
  Purchase #4 $94.69   11.664%   $105.7346   $105.73   $105.75   $105.70  
  Purchase #5 $193.73   5.263%   $203.926   $203.93   $203.95   $203.90  
  Purchase #6 $109.78   11.111%   $121.9777   $121.98   $122.00   $122.00  
  Purchase #7 $216.33   11.728%   $241.7012   $241.70   $241.70   $241.70  
  7 purchase totals = $1,121.85       $1,227.8006   $1,227.80   $1,227.85   $1,227.70