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 $7.59   12.291%   $8.5229   $8.52   $8.50   $8.50  
  Purchase #2 $245.57   5.389%   $258.8038   $258.80   $258.80   $258.80  
  Purchase #3 $180.34   5.823%   $190.8412   $190.84   $190.85   $190.80  
  Purchase #4 $176.99   9.174%   $193.2271   $193.23   $193.25   $193.20  
  Purchase #5 $242.38   9.351%   $265.045   $265.05   $265.05   $265.00  
  Purchase #6 $39.63   4.141%   $41.2711   $41.27   $41.25   $41.30  
  Purchase #7 $65.96   12.658%   $74.3092   $74.31   $74.30   $74.30  
  7 purchase totals = $958.46       $1,032.0203   $1,032.02   $1,032.00   $1,031.90