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 $180.35   8.654%   $195.9575   $195.96   $195.95   $196.00  
  Purchase #2 $184.62   7.703%   $198.8413   $198.84   $198.85   $198.80  
  Purchase #3 $72.60   9.443%   $79.4556   $79.46   $79.45   $79.50  
  Purchase #4 $29.79   8.534%   $32.3323   $32.33   $32.35   $32.30  
  Purchase #5 $63.77   4.758%   $66.8042   $66.80   $66.80   $66.80  
  Purchase #6 $138.92   12.185%   $155.8474   $155.85   $155.85   $155.80  
  Purchase #7 $83.33   11.672%   $93.0563   $93.06   $93.05   $93.10  
  7 purchase totals = $753.38       $822.2946   $822.30   $822.30   $822.30