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 $55.52   9.280%   $60.6723   $60.67   $60.65   $60.70  
  Purchase #2 $219.63   11.123%   $244.0594   $244.06   $244.05   $244.10  
  Purchase #3 $130.40   9.657%   $142.9927   $142.99   $143.00   $143.00  
  Purchase #4 $228.44   3.574%   $236.6044   $236.60   $236.60   $236.60  
  Purchase #5 $159.46   7.777%   $171.8612   $171.86   $171.85   $171.90  
  Purchase #6 $127.42   5.290%   $134.1605   $134.16   $134.15   $134.20  
  Purchase #7 $46.97   5.487%   $49.5472   $49.55   $49.55   $49.50  
  7 purchase totals = $967.84       $1,039.8977   $1,039.89   $1,039.85   $1,040.00