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 $47.45   4.660%   $49.6612   $49.66   $49.65   $49.70  
  Purchase #2 $193.97   13.430%   $220.0202   $220.02   $220.00   $220.00  
  Purchase #3 $184.76   9.238%   $201.8281   $201.83   $201.85   $201.80  
  Purchase #4 $248.61   9.814%   $273.0086   $273.01   $273.00   $273.00  
  Purchase #5 $45.58   6.612%   $48.5937   $48.59   $48.60   $48.60  
  Purchase #6 $55.35   4.564%   $57.8762   $57.88   $57.90   $57.90  
  Purchase #7 $142.95   5.345%   $150.5907   $150.59   $150.60   $150.60  
  7 purchase totals = $918.67       $1,001.5787   $1,001.58   $1,001.60   $1,001.60