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 $61.90   9.689%   $67.8975   $67.90   $67.90   $67.90  
  Purchase #2 $96.61   8.309%   $104.6373   $104.64   $104.65   $104.60  
  Purchase #3 $6.25   9.328%   $6.833   $6.83   $6.85   $6.80  
  Purchase #4 $94.86   11.297%   $105.5763   $105.58   $105.60   $105.60  
  Purchase #5 $247.73   9.236%   $270.6103   $270.61   $270.60   $270.60  
  Purchase #6 $130.46   11.654%   $145.6638   $145.66   $145.65   $145.70  
  Purchase #7 $70.68   8.616%   $76.7698   $76.77   $76.75   $76.80  
  7 purchase totals = $708.49       $777.9880   $777.99   $778.00   $778.00