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 $115.69   5.322%   $121.847   $121.85   $121.85   $121.80  
  Purchase #2 $205.37   10.634%   $227.209   $227.21   $227.20   $227.20  
  Purchase #3 $219.36   12.406%   $246.5738   $246.57   $246.55   $246.60  
  Purchase #4 $250.93   12.796%   $283.039   $283.04   $283.05   $283.00  
  Purchase #5 $61.88   11.365%   $68.9127   $68.91   $68.90   $68.90  
  Purchase #6 $79.95   9.113%   $87.2358   $87.24   $87.25   $87.20  
  Purchase #7 $33.34   3.824%   $34.6149   $34.61   $34.60   $34.60  
  7 purchase totals = $966.52       $1,069.4322   $1,069.43   $1,069.40   $1,069.30