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 $55.68   10.613%   $61.5893   $61.59   $61.60   $61.60  
  Purchase #2 $154.96   3.317%   $160.1   $160.10   $160.10   $160.10  
  Purchase #3 $240.28   13.704%   $273.208   $273.21   $273.20   $273.20  
  Purchase #4 $184.30   8.201%   $199.4144   $199.41   $199.40   $199.40  
  Purchase #5 $122.53   3.454%   $126.7622   $126.76   $126.75   $126.80  
  Purchase #6 $160.26   10.472%   $177.0424   $177.04   $177.05   $177.00  
  Purchase #7 $6.46   11.302%   $7.1901   $7.19   $7.20   $7.20  
  7 purchase totals = $924.47       $1,005.3064   $1,005.30   $1,005.30   $1,005.30