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 $198.44   6.593%   $211.5231   $211.52   $211.50   $211.50  
  Purchase #2 $54.56   9.298%   $59.633   $59.63   $59.65   $59.60  
  Purchase #3 $249.89   5.238%   $262.9792   $262.98   $263.00   $263.00  
  Purchase #4 $191.59   3.704%   $198.6865   $198.69   $198.70   $198.70  
  Purchase #5 $246.26   9.338%   $269.2558   $269.26   $269.25   $269.30  
  Purchase #6 $153.79   6.482%   $163.7587   $163.76   $163.75   $163.80  
  Purchase #7 $72.70   12.729%   $81.954   $81.95   $81.95   $82.00  
  7 purchase totals = $1,167.23       $1,247.7903   $1,247.79   $1,247.80   $1,247.90