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 $88.86   3.363%   $91.8484   $91.85   $91.85   $91.80  
  Purchase #2 $203.66   11.617%   $227.3192   $227.32   $227.30   $227.30  
  Purchase #3 $249.53   5.603%   $263.5112   $263.51   $263.50   $263.50  
  Purchase #4 $232.80   8.801%   $253.2887   $253.29   $253.30   $253.30  
  Purchase #5 $202.44   6.637%   $215.8759   $215.88   $215.90   $215.90  
  Purchase #6 $191.61   4.723%   $200.6597   $200.66   $200.65   $200.70  
  Purchase #7 $201.78   12.770%   $227.5473   $227.55   $227.55   $227.50  
  7 purchase totals = $1,370.68       $1,480.0504   $1,480.06   $1,480.05   $1,480.00