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 $208.79   11.128%   $232.0242   $232.02   $232.00   $232.00  
  Purchase #2 $108.82   4.336%   $113.5384   $113.54   $113.55   $113.50  
  Purchase #3 $65.33   11.745%   $73.003   $73.00   $73.00   $73.00  
  Purchase #4 $215.40   6.332%   $229.0391   $229.04   $229.05   $229.00  
  Purchase #5 $181.69   8.197%   $196.5831   $196.58   $196.60   $196.60  
  Purchase #6 $179.91   12.794%   $202.9277   $202.93   $202.95   $202.90  
  Purchase #7 $205.63   6.639%   $219.2818   $219.28   $219.30   $219.30  
  7 purchase totals = $1,165.57       $1,266.3973   $1,266.39   $1,266.45   $1,266.30