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 $60.63   11.625%   $67.6782   $67.68   $67.70   $67.70  
  Purchase #2 $42.58   3.235%   $43.9575   $43.96   $43.95   $44.00  
  Purchase #3 $83.52   7.278%   $89.5986   $89.60   $89.60   $89.60  
  Purchase #4 $118.26   5.279%   $124.5029   $124.50   $124.50   $124.50  
  Purchase #5 $245.96   12.306%   $276.2278   $276.23   $276.25   $276.20  
  Purchase #6 $166.53   12.404%   $187.1864   $187.19   $187.20   $187.20  
  Purchase #7 $188.64   3.581%   $195.3952   $195.40   $195.40   $195.40  
  7 purchase totals = $906.12       $984.5466   $984.56   $984.60   $984.60