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 $248.35   11.776%   $277.5957   $277.60   $277.60   $277.60  
  Purchase #2 $181.72   7.484%   $195.3199   $195.32   $195.30   $195.30  
  Purchase #3 $63.52   4.291%   $66.2456   $66.25   $66.25   $66.20  
  Purchase #4 $131.41   4.323%   $137.0909   $137.09   $137.10   $137.10  
  Purchase #5 $103.44   8.821%   $112.5644   $112.56   $112.55   $112.60  
  Purchase #6 $187.77   8.171%   $203.1127   $203.11   $203.10   $203.10  
  Purchase #7 $221.71   8.828%   $241.2826   $241.28   $241.30   $241.30  
  7 purchase totals = $1,137.92       $1,233.2118   $1,233.21   $1,233.20   $1,233.20