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 $96.27   8.489%   $104.4424   $104.44   $104.45   $104.40  
  Purchase #2 $114.70   13.838%   $130.5722   $130.57   $130.55   $130.60  
  Purchase #3 $211.67   6.795%   $226.053   $226.05   $226.05   $226.10  
  Purchase #4 $44.82   12.658%   $50.4933   $50.49   $50.50   $50.50  
  Purchase #5 $91.33   9.205%   $99.7369   $99.74   $99.75   $99.70  
  Purchase #6 $88.27   4.534%   $92.2722   $92.27   $92.25   $92.30  
  Purchase #7 $63.40   9.653%   $69.52   $69.52   $69.50   $69.50  
  7 purchase totals = $710.46       $773.0900   $773.08   $773.05   $773.10