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 $52.77   8.265%   $57.1314   $57.13   $57.15   $57.10  
  Purchase #2 $230.92   5.418%   $243.4312   $243.43   $243.45   $243.40  
  Purchase #3 $40.92   8.128%   $44.246   $44.25   $44.25   $44.20  
  Purchase #4 $187.78   10.149%   $206.8378   $206.84   $206.85   $206.80  
  Purchase #5 $204.67   11.133%   $227.4559   $227.46   $227.45   $227.50  
  Purchase #6 $110.64   8.550%   $120.0997   $120.10   $120.10   $120.10  
  Purchase #7 $236.65   6.514%   $252.0654   $252.07   $252.05   $252.10  
  7 purchase totals = $1,064.35       $1,151.2674   $1,151.28   $1,151.30   $1,151.20