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 $97.39   13.649%   $110.6828   $110.68   $110.70   $110.70  
  Purchase #2 $234.94   13.621%   $266.9412   $266.94   $266.95   $266.90  
  Purchase #3 $112.68   9.351%   $123.2167   $123.22   $123.20   $123.20  
  Purchase #4 $194.74   3.292%   $201.1508   $201.15   $201.15   $201.20  
  Purchase #5 $41.95   6.342%   $44.6105   $44.61   $44.60   $44.60  
  Purchase #6 $113.57   4.870%   $119.1009   $119.10   $119.10   $119.10  
  Purchase #7 $7.74   3.443%   $8.0065   $8.01   $8.00   $8.00  
  7 purchase totals = $803.01       $873.7094   $873.71   $873.70   $873.70