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 $118.69   12.130%   $133.0871   $133.09   $133.10   $133.10  
  Purchase #2 $87.53   5.867%   $92.6654   $92.67   $92.65   $92.70  
  Purchase #3 $53.35   11.598%   $59.5375   $59.54   $59.55   $59.50  
  Purchase #4 $174.27   6.371%   $185.3727   $185.37   $185.35   $185.40  
  Purchase #5 $231.90   13.134%   $262.3577   $262.36   $262.35   $262.40  
  Purchase #6 $184.64   3.830%   $191.7117   $191.71   $191.70   $191.70  
  Purchase #7 $228.65   12.492%   $257.213   $257.21   $257.20   $257.20  
  7 purchase totals = $1,079.03       $1,181.9451   $1,181.95   $1,181.90   $1,182.00