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 $212.66   11.307%   $236.7055   $236.71   $236.70   $236.70  
  Purchase #2 $159.26   4.634%   $166.6401   $166.64   $166.65   $166.60  
  Purchase #3 $165.27   13.779%   $188.0426   $188.04   $188.05   $188.00  
  Purchase #4 $208.65   7.827%   $224.981   $224.98   $225.00   $225.00  
  Purchase #5 $187.41   5.743%   $198.173   $198.17   $198.15   $198.20  
  Purchase #6 $37.37   10.621%   $41.3391   $41.34   $41.35   $41.30  
  Purchase #7 $9.30   6.582%   $9.9121   $9.91   $9.90   $9.90  
  7 purchase totals = $979.92       $1,065.7934   $1,065.79   $1,065.80   $1,065.70