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 $241.69   7.841%   $260.6409   $260.64   $260.65   $260.60  
  Purchase #2 $167.48   4.745%   $175.4269   $175.43   $175.45   $175.40  
  Purchase #3 $61.64   5.533%   $65.0505   $65.05   $65.05   $65.10  
  Purchase #4 $235.40   11.633%   $262.7841   $262.78   $262.80   $262.80  
  Purchase #5 $132.39   12.685%   $149.1837   $149.18   $149.20   $149.20  
  Purchase #6 $213.46   10.689%   $236.2767   $236.28   $236.30   $236.30  
  Purchase #7 $96.57   7.572%   $103.8823   $103.88   $103.90   $103.90  
  7 purchase totals = $1,148.63       $1,253.2451   $1,253.24   $1,253.35   $1,253.30