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 $246.62   8.331%   $267.1659   $267.17   $267.15   $267.20  
  Purchase #2 $89.30   7.132%   $95.6689   $95.67   $95.65   $95.70  
  Purchase #3 $108.84   11.229%   $121.0616   $121.06   $121.05   $121.10  
  Purchase #4 $200.81   11.873%   $224.6522   $224.65   $224.65   $224.70  
  Purchase #5 $232.40   4.391%   $242.6047   $242.60   $242.60   $242.60  
  Purchase #6 $116.36   12.366%   $130.7491   $130.75   $130.75   $130.70  
  Purchase #7 $201.59   5.242%   $212.1573   $212.16   $212.15   $212.20  
  7 purchase totals = $1,195.92       $1,294.0597   $1,294.06   $1,294.00   $1,294.20