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 $204.27   10.303%   $225.3159   $225.32   $225.30   $225.30  
  Purchase #2 $161.84   9.237%   $176.7892   $176.79   $176.80   $176.80  
  Purchase #3 $120.30   11.445%   $134.0683   $134.07   $134.05   $134.10  
  Purchase #4 $43.78   12.565%   $49.281   $49.28   $49.30   $49.30  
  Purchase #5 $101.74   5.466%   $107.3011   $107.30   $107.30   $107.30  
  Purchase #6 $216.83   10.702%   $240.0351   $240.04   $240.05   $240.00  
  Purchase #7 $215.61   6.771%   $230.209   $230.21   $230.20   $230.20  
  7 purchase totals = $1,064.37       $1,162.9996   $1,163.01   $1,163.00   $1,163.00