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 $206.65   5.621%   $218.2658   $218.27   $218.25   $218.30  
  Purchase #2 $231.32   13.775%   $263.1843   $263.18   $263.20   $263.20  
  Purchase #3 $16.90   6.451%   $17.9902   $17.99   $18.00   $18.00  
  Purchase #4 $54.28   6.568%   $57.8451   $57.85   $57.85   $57.80  
  Purchase #5 $190.50   11.268%   $211.9655   $211.97   $211.95   $212.00  
  Purchase #6 $53.68   10.497%   $59.3148   $59.31   $59.30   $59.30  
  Purchase #7 $222.79   6.393%   $237.033   $237.03   $237.05   $237.00  
  7 purchase totals = $976.12       $1,065.5987   $1,065.60   $1,065.60   $1,065.60