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 $49.74   12.514%   $55.9645   $55.96   $55.95   $56.00  
  Purchase #2 $212.43   3.699%   $220.2878   $220.29   $220.30   $220.30  
  Purchase #3 $37.85   8.385%   $41.0237   $41.02   $41.00   $41.00  
  Purchase #4 $52.55   9.408%   $57.4939   $57.49   $57.50   $57.50  
  Purchase #5 $207.87   9.669%   $227.969   $227.97   $227.95   $228.00  
  Purchase #6 $44.62   9.167%   $48.7103   $48.71   $48.70   $48.70  
  Purchase #7 $124.66   3.532%   $129.063   $129.06   $129.05   $129.10  
  7 purchase totals = $729.72       $780.5122   $780.50   $780.45   $780.60