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 $60.81   13.647%   $69.1087   $69.11   $69.10   $69.10  
  Purchase #2 $164.81   10.104%   $181.4624   $181.46   $181.45   $181.50  
  Purchase #3 $224.84   6.182%   $238.7396   $238.74   $238.75   $238.70  
  Purchase #4 $99.98   6.172%   $106.1508   $106.15   $106.15   $106.20  
  Purchase #5 $147.44   11.332%   $164.1479   $164.15   $164.15   $164.10  
  Purchase #6 $216.96   8.106%   $234.5468   $234.55   $234.55   $234.50  
  Purchase #7 $29.31   4.355%   $30.5865   $30.59   $30.60   $30.60  
  7 purchase totals = $944.15       $1,024.7427   $1,024.75   $1,024.75   $1,024.70