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 $164.91   10.871%   $182.8374   $182.84   $182.85   $182.80  
  Purchase #2 $219.52   7.296%   $235.5362   $235.54   $235.55   $235.50  
  Purchase #3 $241.87   4.716%   $253.2766   $253.28   $253.30   $253.30  
  Purchase #4 $21.25   11.564%   $23.7074   $23.71   $23.70   $23.70  
  Purchase #5 $181.85   10.304%   $200.5878   $200.59   $200.60   $200.60  
  Purchase #6 $91.99   4.672%   $96.2878   $96.29   $96.30   $96.30  
  Purchase #7 $30.65   6.363%   $32.6003   $32.60   $32.60   $32.60  
  7 purchase totals = $952.04       $1,024.8335   $1,024.85   $1,024.90   $1,024.80