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 $221.56   9.529%   $242.6725   $242.67   $242.65   $242.70  
  Purchase #2 $242.62   5.523%   $256.0199   $256.02   $256.00   $256.00  
  Purchase #3 $88.62   11.445%   $98.7626   $98.76   $98.75   $98.80  
  Purchase #4 $212.79   8.173%   $230.1813   $230.18   $230.20   $230.20  
  Purchase #5 $152.28   13.159%   $172.3185   $172.32   $172.30   $172.30  
  Purchase #6 $201.55   5.382%   $212.3974   $212.40   $212.40   $212.40  
  Purchase #7 $145.44   6.497%   $154.8892   $154.89   $154.90   $154.90  
  7 purchase totals = $1,264.86       $1,367.2414   $1,367.24   $1,367.20   $1,367.30