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 $91.78   5.557%   $96.8802   $96.88   $96.90   $96.90  
  Purchase #2 $15.68   6.523%   $16.7028   $16.70   $16.70   $16.70  
  Purchase #3 $55.55   11.817%   $62.1143   $62.11   $62.10   $62.10  
  Purchase #4 $81.62   13.436%   $92.5865   $92.59   $92.60   $92.60  
  Purchase #5 $159.50   10.595%   $176.399   $176.40   $176.40   $176.40  
  Purchase #6 $180.61   8.585%   $196.1154   $196.12   $196.10   $196.10  
  Purchase #7 $216.70   13.812%   $246.6306   $246.63   $246.65   $246.60  
  7 purchase totals = $801.44       $887.4288   $887.43   $887.45   $887.40