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 $66.57   5.809%   $70.4371   $70.44   $70.45   $70.40  
  Purchase #2 $244.43   8.434%   $265.0452   $265.05   $265.05   $265.00  
  Purchase #3 $234.36   3.434%   $242.4079   $242.41   $242.40   $242.40  
  Purchase #4 $64.53   6.774%   $68.9013   $68.90   $68.90   $68.90  
  Purchase #5 $167.72   7.500%   $180.299   $180.30   $180.30   $180.30  
  Purchase #6 $153.95   8.602%   $167.1928   $167.19   $167.20   $167.20  
  Purchase #7 $159.91   5.638%   $168.9257   $168.93   $168.95   $168.90  
  7 purchase totals = $1,091.47       $1,163.2090   $1,163.22   $1,163.25   $1,163.10