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 $69.87   7.496%   $75.1075   $75.11   $75.10   $75.10  
  Purchase #2 $143.77   9.158%   $156.9365   $156.94   $156.95   $156.90  
  Purchase #3 $159.53   4.792%   $167.1747   $167.17   $167.15   $167.20  
  Purchase #4 $233.72   9.693%   $256.3745   $256.37   $256.35   $256.40  
  Purchase #5 $55.65   4.698%   $58.2644   $58.26   $58.25   $58.30  
  Purchase #6 $181.32   10.609%   $200.5562   $200.56   $200.55   $200.60  
  Purchase #7 $138.45   10.771%   $153.3624   $153.36   $153.35   $153.40  
  7 purchase totals = $982.31       $1,067.7762   $1,067.77   $1,067.70   $1,067.90