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 $63.91   7.811%   $68.902   $68.90   $68.90   $68.90  
  Purchase #2 $91.57   13.558%   $103.9851   $103.99   $104.00   $104.00  
  Purchase #3 $82.66   3.303%   $85.3903   $85.39   $85.40   $85.40  
  Purchase #4 $243.88   4.171%   $254.0522   $254.05   $254.05   $254.10  
  Purchase #5 $151.40   9.633%   $165.9844   $165.98   $166.00   $166.00  
  Purchase #6 $62.42   5.622%   $65.9293   $65.93   $65.95   $65.90  
  Purchase #7 $248.50   4.142%   $258.7929   $258.79   $258.80   $258.80  
  7 purchase totals = $944.34       $1,003.0362   $1,003.03   $1,003.10   $1,003.10