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 $75.33   12.552%   $84.7854   $84.79   $84.80   $84.80  
  Purchase #2 $173.93   10.523%   $192.2327   $192.23   $192.25   $192.20  
  Purchase #3 $32.66   7.160%   $34.9985   $35.00   $35.00   $35.00  
  Purchase #4 $123.44   10.536%   $136.4456   $136.45   $136.45   $136.40  
  Purchase #5 $150.49   7.779%   $162.1966   $162.20   $162.20   $162.20  
  Purchase #6 $13.45   5.764%   $14.2253   $14.23   $14.25   $14.20  
  Purchase #7 $117.42   7.813%   $126.594   $126.59   $126.60   $126.60  
  7 purchase totals = $686.72       $751.4781   $751.49   $751.55   $751.40