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 $22.53   9.294%   $24.6239   $24.62   $24.60   $24.60  
  Purchase #2 $220.92   12.764%   $249.1182   $249.12   $249.10   $249.10  
  Purchase #3 $47.81   12.320%   $53.7002   $53.70   $53.70   $53.70  
  Purchase #4 $214.99   6.419%   $228.7902   $228.79   $228.80   $228.80  
  Purchase #5 $22.92   6.238%   $24.3497   $24.35   $24.35   $24.30  
  Purchase #6 $225.58   13.641%   $256.3514   $256.35   $256.35   $256.40  
  Purchase #7 $126.72   9.555%   $138.8281   $138.83   $138.85   $138.80  
  7 purchase totals = $881.47       $975.7617   $975.76   $975.75   $975.70