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 $228.39   5.539%   $241.0405   $241.04   $241.05   $241.00  
  Purchase #2 $166.67   10.710%   $184.5204   $184.52   $184.50   $184.50  
  Purchase #3 $241.64   3.562%   $250.2472   $250.25   $250.25   $250.20  
  Purchase #4 $18.33   5.113%   $19.2672   $19.27   $19.25   $19.30  
  Purchase #5 $127.31   10.632%   $140.8456   $140.85   $140.85   $140.80  
  Purchase #6 $139.81   10.306%   $154.2188   $154.22   $154.20   $154.20  
  Purchase #7 $108.64   3.317%   $112.2436   $112.24   $112.25   $112.20  
  7 purchase totals = $1,030.79       $1,102.3833   $1,102.39   $1,102.35   $1,102.20