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 $86.98   10.404%   $96.0294   $96.03   $96.05   $96.00  
  Purchase #2 $37.76   11.306%   $42.0291   $42.03   $42.05   $42.00  
  Purchase #3 $61.68   9.576%   $67.5865   $67.59   $67.60   $67.60  
  Purchase #4 $117.70   5.124%   $123.7309   $123.73   $123.75   $123.70  
  Purchase #5 $211.83   4.607%   $221.589   $221.59   $221.60   $221.60  
  Purchase #6 $69.76   7.850%   $75.2362   $75.24   $75.25   $75.20  
  Purchase #7 $168.99   6.365%   $179.7462   $179.75   $179.75   $179.70  
  7 purchase totals = $754.70       $805.9473   $805.96   $806.05   $805.80