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 $67.29   13.274%   $76.2221   $76.22   $76.20   $76.20  
  Purchase #2 $69.61   7.708%   $74.9755   $74.98   $75.00   $75.00  
  Purchase #3 $159.44   6.850%   $170.3616   $170.36   $170.35   $170.40  
  Purchase #4 $207.35   7.368%   $222.6275   $222.63   $222.65   $222.60  
  Purchase #5 $220.65   3.493%   $228.3573   $228.36   $228.35   $228.40  
  Purchase #6 $222.76   12.577%   $250.7765   $250.78   $250.80   $250.80  
  Purchase #7 $61.43   5.564%   $64.848   $64.85   $64.85   $64.80  
  7 purchase totals = $1,008.53       $1,088.1685   $1,088.18   $1,088.20   $1,088.20