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 $159.36   10.320%   $175.806   $175.81   $175.80   $175.80  
  Purchase #2 $187.33   4.550%   $195.8535   $195.85   $195.85   $195.90  
  Purchase #3 $159.93   4.261%   $166.7446   $166.74   $166.75   $166.70  
  Purchase #4 $244.86   8.600%   $265.918   $265.92   $265.90   $265.90  
  Purchase #5 $12.64   8.724%   $13.7427   $13.74   $13.75   $13.70  
  Purchase #6 $97.61   5.495%   $102.9737   $102.97   $102.95   $103.00  
  Purchase #7 $153.30   12.523%   $172.4978   $172.50   $172.50   $172.50  
  7 purchase totals = $1,015.03       $1,093.5363   $1,093.53   $1,093.50   $1,093.50