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 $229.65   8.716%   $249.6663   $249.67   $249.65   $249.70  
  Purchase #2 $218.31   8.560%   $236.9973   $237.00   $237.00   $237.00  
  Purchase #3 $221.85   8.108%   $239.8376   $239.84   $239.85   $239.80  
  Purchase #4 $215.68   5.841%   $228.2779   $228.28   $228.30   $228.30  
  Purchase #5 $141.59   13.866%   $161.2229   $161.22   $161.20   $161.20  
  Purchase #6 $22.84   6.617%   $24.3513   $24.35   $24.35   $24.40  
  Purchase #7 $113.89   11.476%   $126.96   $126.96   $126.95   $127.00  
  7 purchase totals = $1,163.81       $1,267.3133   $1,267.32   $1,267.30   $1,267.40