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 $88.26   11.285%   $98.2201   $98.22   $98.20   $98.20  
  Purchase #2 $87.93   8.485%   $95.3909   $95.39   $95.40   $95.40  
  Purchase #3 $165.34   3.792%   $171.6097   $171.61   $171.60   $171.60  
  Purchase #4 $39.61   11.552%   $44.1857   $44.19   $44.20   $44.20  
  Purchase #5 $36.50   11.220%   $40.5953   $40.60   $40.60   $40.60  
  Purchase #6 $223.67   7.777%   $241.0648   $241.06   $241.05   $241.10  
  Purchase #7 $106.65   7.544%   $114.6957   $114.70   $114.70   $114.70  
  7 purchase totals = $747.96       $805.7622   $805.77   $805.75   $805.80