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 $89.74   4.190%   $93.5001   $93.50   $93.50   $93.50  
  Purchase #2 $170.96   7.672%   $184.0761   $184.08   $184.10   $184.10  
  Purchase #3 $119.57   12.757%   $134.8235   $134.82   $134.80   $134.80  
  Purchase #4 $164.91   10.226%   $181.7737   $181.77   $181.75   $181.80  
  Purchase #5 $114.78   8.768%   $124.8439   $124.84   $124.85   $124.80  
  Purchase #6 $213.48   3.549%   $221.0564   $221.06   $221.05   $221.10  
  Purchase #7 $79.82   6.327%   $84.8702   $84.87   $84.85   $84.90  
  7 purchase totals = $953.26       $1,024.9439   $1,024.94   $1,024.90   $1,025.00