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 $158.29   8.357%   $171.5183   $171.52   $171.50   $171.50  
  Purchase #2 $238.87   3.657%   $247.6055   $247.61   $247.60   $247.60  
  Purchase #3 $216.76   3.368%   $224.0605   $224.06   $224.05   $224.10  
  Purchase #4 $170.66   10.485%   $188.5537   $188.55   $188.55   $188.60  
  Purchase #5 $218.60   3.548%   $226.3559   $226.36   $226.35   $226.40  
  Purchase #6 $219.48   5.574%   $231.7138   $231.71   $231.70   $231.70  
  Purchase #7 $184.67   10.603%   $204.2506   $204.25   $204.25   $204.30  
  7 purchase totals = $1,407.33       $1,494.0583   $1,494.06   $1,494.00   $1,494.20