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 $46.96   4.229%   $48.9459   $48.95   $48.95   $48.90  
  Purchase #2 $117.42   11.565%   $130.9996   $131.00   $131.00   $131.00  
  Purchase #3 $211.35   12.623%   $238.0287   $238.03   $238.05   $238.00  
  Purchase #4 $105.68   3.871%   $109.7709   $109.77   $109.75   $109.80  
  Purchase #5 $179.90   8.791%   $195.715   $195.72   $195.70   $195.70  
  Purchase #6 $80.50   4.529%   $84.1458   $84.15   $84.15   $84.10  
  Purchase #7 $179.60   9.496%   $196.6548   $196.65   $196.65   $196.70  
  7 purchase totals = $921.41       $1,004.2607   $1,004.27   $1,004.25   $1,004.20