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 $242.91   13.725%   $276.2494   $276.25   $276.25   $276.20  
  Purchase #2 $22.71   6.214%   $24.1212   $24.12   $24.10   $24.10  
  Purchase #3 $235.77   13.793%   $268.2898   $268.29   $268.30   $268.30  
  Purchase #4 $203.29   8.275%   $220.1122   $220.11   $220.10   $220.10  
  Purchase #5 $152.57   12.420%   $171.5192   $171.52   $171.50   $171.50  
  Purchase #6 $31.41   8.299%   $34.0167   $34.02   $34.00   $34.00  
  Purchase #7 $27.98   13.267%   $31.6921   $31.69   $31.70   $31.70  
  7 purchase totals = $916.64       $1,026.0006   $1,026.00   $1,025.95   $1,025.90