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 $224.76   8.465%   $243.7859   $243.79   $243.80   $243.80  
  Purchase #2 $203.31   6.170%   $215.8542   $215.85   $215.85   $215.90  
  Purchase #3 $222.55   4.352%   $232.2354   $232.24   $232.25   $232.20  
  Purchase #4 $197.38   9.538%   $216.2061   $216.21   $216.20   $216.20  
  Purchase #5 $185.83   11.575%   $207.3398   $207.34   $207.35   $207.30  
  Purchase #6 $24.92   8.197%   $26.9627   $26.96   $26.95   $27.00  
  Purchase #7 $178.86   9.753%   $196.3042   $196.30   $196.30   $196.30  
  7 purchase totals = $1,237.61       $1,338.6883   $1,338.69   $1,338.70   $1,338.70