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 $232.98   13.861%   $265.2734   $265.27   $265.25   $265.30  
  Purchase #2 $53.96   12.156%   $60.5194   $60.52   $60.50   $60.50  
  Purchase #3 $64.45   8.577%   $69.9779   $69.98   $70.00   $70.00  
  Purchase #4 $109.36   7.171%   $117.2022   $117.20   $117.20   $117.20  
  Purchase #5 $199.25   12.613%   $224.3814   $224.38   $224.40   $224.40  
  Purchase #6 $160.63   4.613%   $168.0399   $168.04   $168.05   $168.00  
  Purchase #7 $173.73   7.750%   $187.1941   $187.19   $187.20   $187.20  
  7 purchase totals = $994.36       $1,092.5883   $1,092.58   $1,092.60   $1,092.60