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 $64.95   5.858%   $68.7548   $68.75   $68.75   $68.80  
  Purchase #2 $157.77   11.778%   $176.3522   $176.35   $176.35   $176.40  
  Purchase #3 $188.91   7.847%   $203.7338   $203.73   $203.75   $203.70  
  Purchase #4 $224.78   10.641%   $248.6988   $248.70   $248.70   $248.70  
  Purchase #5 $179.26   4.814%   $187.8896   $187.89   $187.90   $187.90  
  Purchase #6 $174.80   11.152%   $194.2937   $194.29   $194.30   $194.30  
  Purchase #7 $177.56   7.481%   $190.8433   $190.84   $190.85   $190.80  
  7 purchase totals = $1,168.03       $1,270.5662   $1,270.55   $1,270.60   $1,270.60