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 $235.73   10.326%   $260.0715   $260.07   $260.05   $260.10  
  Purchase #2 $41.81   13.839%   $47.5961   $47.60   $47.60   $47.60  
  Purchase #3 $116.94   13.349%   $132.5503   $132.55   $132.55   $132.60  
  Purchase #4 $192.71   7.683%   $207.5159   $207.52   $207.50   $207.50  
  Purchase #5 $124.54   3.325%   $128.681   $128.68   $128.70   $128.70  
  Purchase #6 $208.51   4.587%   $218.0744   $218.07   $218.05   $218.10  
  Purchase #7 $224.68   6.214%   $238.6416   $238.64   $238.65   $238.60  
  7 purchase totals = $1,144.92       $1,233.1308   $1,233.13   $1,233.10   $1,233.20