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 $39.80   9.861%   $43.7247   $43.72   $43.70   $43.70  
  Purchase #2 $52.67   11.311%   $58.6275   $58.63   $58.65   $58.60  
  Purchase #3 $211.70   7.216%   $226.9763   $226.98   $227.00   $227.00  
  Purchase #4 $141.89   12.537%   $159.6787   $159.68   $159.70   $159.70  
  Purchase #5 $74.78   13.412%   $84.8095   $84.81   $84.80   $84.80  
  Purchase #6 $247.74   9.423%   $271.0845   $271.08   $271.10   $271.10  
  Purchase #7 $14.59   12.839%   $16.4632   $16.46   $16.45   $16.50  
  7 purchase totals = $783.17       $861.3644   $861.36   $861.40   $861.40