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 $184.48   3.442%   $190.8298   $190.83   $190.85   $190.80  
  Purchase #2 $73.84   3.183%   $76.1903   $76.19   $76.20   $76.20  
  Purchase #3 $215.70   6.405%   $229.5156   $229.52   $229.50   $229.50  
  Purchase #4 $250.67   7.642%   $269.8262   $269.83   $269.85   $269.80  
  Purchase #5 $250.37   9.285%   $273.6169   $273.62   $273.60   $273.60  
  Purchase #6 $57.97   3.745%   $60.141   $60.14   $60.15   $60.10  
  Purchase #7 $21.98   3.290%   $22.7031   $22.70   $22.70   $22.70  
  7 purchase totals = $1,055.01       $1,122.8229   $1,122.83   $1,122.85   $1,122.70