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 $96.54   12.283%   $108.398   $108.40   $108.40   $108.40  
  Purchase #2 $151.36   4.364%   $157.9654   $157.97   $157.95   $158.00  
  Purchase #3 $211.25   8.299%   $228.7816   $228.78   $228.80   $228.80  
  Purchase #4 $63.92   12.445%   $71.8748   $71.87   $71.85   $71.90  
  Purchase #5 $82.83   9.483%   $90.6848   $90.68   $90.70   $90.70  
  Purchase #6 $143.70   4.686%   $150.4338   $150.43   $150.45   $150.40  
  Purchase #7 $235.67   7.283%   $252.8338   $252.83   $252.85   $252.80  
  7 purchase totals = $985.27       $1,060.9722   $1,060.96   $1,061.00   $1,061.00