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 $44.94   10.482%   $49.6506   $49.65   $49.65   $49.70  
  Purchase #2 $229.28   10.183%   $252.6276   $252.63   $252.65   $252.60  
  Purchase #3 $221.88   3.138%   $228.8426   $228.84   $228.85   $228.80  
  Purchase #4 $168.25   9.870%   $184.8563   $184.86   $184.85   $184.90  
  Purchase #5 $246.84   12.232%   $277.0335   $277.03   $277.05   $277.00  
  Purchase #6 $83.89   5.269%   $88.3102   $88.31   $88.30   $88.30  
  Purchase #7 $232.61   12.428%   $261.5188   $261.52   $261.50   $261.50  
  7 purchase totals = $1,227.69       $1,342.8396   $1,342.84   $1,342.85   $1,342.80