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 $215.35   8.511%   $233.6784   $233.68   $233.70   $233.70  
  Purchase #2 $104.59   3.109%   $107.8417   $107.84   $107.85   $107.80  
  Purchase #3 $80.41   13.774%   $91.4857   $91.49   $91.50   $91.50  
  Purchase #4 $63.66   6.588%   $67.8539   $67.85   $67.85   $67.90  
  Purchase #5 $14.59   6.603%   $15.5534   $15.55   $15.55   $15.60  
  Purchase #6 $212.52   6.387%   $226.0937   $226.09   $226.10   $226.10  
  Purchase #7 $243.47   9.150%   $265.7475   $265.75   $265.75   $265.70  
  7 purchase totals = $934.59       $1,008.2543   $1,008.25   $1,008.30   $1,008.30