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 $163.91   10.503%   $181.1255   $181.13   $181.15   $181.10  
  Purchase #2 $114.98   12.288%   $129.1087   $129.11   $129.10   $129.10  
  Purchase #3 $232.53   7.119%   $249.0838   $249.08   $249.10   $249.10  
  Purchase #4 $106.70   11.203%   $118.6536   $118.65   $118.65   $118.70  
  Purchase #5 $143.81   10.520%   $158.9388   $158.94   $158.95   $158.90  
  Purchase #6 $31.68   9.824%   $34.7922   $34.79   $34.80   $34.80  
  Purchase #7 $111.55   5.168%   $117.3149   $117.31   $117.30   $117.30  
  7 purchase totals = $905.16       $989.0175   $989.01   $989.05   $989.00