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 $115.73   3.267%   $119.5109   $119.51   $119.50   $119.50  
  Purchase #2 $49.28   7.643%   $53.0465   $53.05   $53.05   $53.00  
  Purchase #3 $64.75   6.570%   $69.0041   $69.00   $69.00   $69.00  
  Purchase #4 $229.52   3.469%   $237.482   $237.48   $237.50   $237.50  
  Purchase #5 $39.68   5.160%   $41.7275   $41.73   $41.75   $41.70  
  Purchase #6 $11.46   8.504%   $12.4346   $12.43   $12.45   $12.40  
  Purchase #7 $196.77   8.453%   $213.403   $213.40   $213.40   $213.40  
  7 purchase totals = $707.19       $746.6086   $746.60   $746.65   $746.50