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 $66.39   13.517%   $75.3639   $75.36   $75.35   $75.40  
  Purchase #2 $223.48   13.171%   $252.9146   $252.91   $252.90   $252.90  
  Purchase #3 $192.82   12.791%   $217.4836   $217.48   $217.50   $217.50  
  Purchase #4 $211.38   12.637%   $238.0921   $238.09   $238.10   $238.10  
  Purchase #5 $165.92   9.609%   $181.8633   $181.86   $181.85   $181.90  
  Purchase #6 $128.51   5.252%   $135.2593   $135.26   $135.25   $135.30  
  Purchase #7 $220.95   12.260%   $248.0385   $248.04   $248.05   $248.00  
  7 purchase totals = $1,209.45       $1,349.0153   $1,349.00   $1,349.00   $1,349.10