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 $250.91   4.756%   $262.8433   $262.84   $262.85   $262.80  
  Purchase #2 $238.39   9.288%   $260.5317   $260.53   $260.55   $260.50  
  Purchase #3 $17.75   9.689%   $19.4698   $19.47   $19.45   $19.50  
  Purchase #4 $184.82   3.108%   $190.5642   $190.56   $190.55   $190.60  
  Purchase #5 $87.65   10.245%   $96.6297   $96.63   $96.65   $96.60  
  Purchase #6 $53.82   9.279%   $58.814   $58.81   $58.80   $58.80  
  Purchase #7 $160.66   9.778%   $176.3693   $176.37   $176.35   $176.40  
  7 purchase totals = $994.00       $1,065.2220   $1,065.21   $1,065.20   $1,065.20