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 $84.71   9.642%   $92.8777   $92.88   $92.90   $92.90  
  Purchase #2 $16.31   7.431%   $17.522   $17.52   $17.50   $17.50  
  Purchase #3 $230.94   6.269%   $245.4176   $245.42   $245.40   $245.40  
  Purchase #4 $112.79   12.460%   $126.8436   $126.84   $126.85   $126.80  
  Purchase #5 $237.71   6.312%   $252.7143   $252.71   $252.70   $252.70  
  Purchase #6 $154.70   6.518%   $164.7833   $164.78   $164.80   $164.80  
  Purchase #7 $108.26   5.155%   $113.8408   $113.84   $113.85   $113.80  
  7 purchase totals = $945.42       $1,013.9993   $1,013.99   $1,014.00   $1,013.90