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 $172.55   5.413%   $181.8901   $181.89   $181.90   $181.90  
  Purchase #2 $84.63   5.451%   $89.2432   $89.24   $89.25   $89.20  
  Purchase #3 $200.60   9.710%   $220.0783   $220.08   $220.10   $220.10  
  Purchase #4 $130.96   7.170%   $140.3498   $140.35   $140.35   $140.30  
  Purchase #5 $19.31   3.598%   $20.0048   $20.00   $20.00   $20.00  
  Purchase #6 $29.42   3.394%   $30.4185   $30.42   $30.40   $30.40  
  Purchase #7 $144.58   7.502%   $155.4264   $155.43   $155.45   $155.40  
  7 purchase totals = $782.05       $837.4111   $837.41   $837.45   $837.30