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 $56.91   10.236%   $62.7353   $62.74   $62.75   $62.70  
  Purchase #2 $14.92   9.366%   $16.3174   $16.32   $16.30   $16.30  
  Purchase #3 $202.90   8.261%   $219.6616   $219.66   $219.65   $219.70  
  Purchase #4 $58.52   8.826%   $63.685   $63.69   $63.70   $63.70  
  Purchase #5 $206.34   6.617%   $219.9935   $219.99   $220.00   $220.00  
  Purchase #6 $177.85   4.823%   $186.4277   $186.43   $186.45   $186.40  
  Purchase #7 $28.99   9.652%   $31.7881   $31.79   $31.80   $31.80  
  7 purchase totals = $746.43       $800.6086   $800.62   $800.65   $800.60