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 $93.79   4.623%   $98.1259   $98.13   $98.15   $98.10  
  Purchase #2 $207.58   11.139%   $230.7023   $230.70   $230.70   $230.70  
  Purchase #3 $202.86   10.233%   $223.6187   $223.62   $223.60   $223.60  
  Purchase #4 $13.90   4.489%   $14.524   $14.52   $14.50   $14.50  
  Purchase #5 $8.78   6.327%   $9.3355   $9.34   $9.35   $9.30  
  Purchase #6 $90.97   4.566%   $95.1237   $95.12   $95.10   $95.10  
  Purchase #7 $101.71   3.656%   $105.4285   $105.43   $105.45   $105.40  
  7 purchase totals = $719.59       $776.8586   $776.86   $776.85   $776.70