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 $107.33   5.183%   $112.8929   $112.89   $112.90   $112.90  
  Purchase #2 $224.91   11.295%   $250.3136   $250.31   $250.30   $250.30  
  Purchase #3 $222.97   5.360%   $234.9212   $234.92   $234.90   $234.90  
  Purchase #4 $16.57   7.519%   $17.8159   $17.82   $17.80   $17.80  
  Purchase #5 $233.73   3.491%   $241.8895   $241.89   $241.90   $241.90  
  Purchase #6 $43.43   4.485%   $45.3778   $45.38   $45.40   $45.40  
  Purchase #7 $189.58   12.824%   $213.8917   $213.89   $213.90   $213.90  
  7 purchase totals = $1,038.52       $1,117.1026   $1,117.10   $1,117.10   $1,117.10