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 $86.30   7.530%   $92.7984   $92.80   $92.80   $92.80  
  Purchase #2 $208.49   8.241%   $225.6717   $225.67   $225.65   $225.70  
  Purchase #3 $105.75   12.469%   $118.936   $118.94   $118.95   $118.90  
  Purchase #4 $24.54   12.242%   $27.5442   $27.54   $27.55   $27.50  
  Purchase #5 $154.32   11.353%   $171.8399   $171.84   $171.85   $171.80  
  Purchase #6 $92.54   6.653%   $98.6967   $98.70   $98.70   $98.70  
  Purchase #7 $82.59   7.110%   $88.4621   $88.46   $88.45   $88.50  
  7 purchase totals = $754.53       $823.9490   $823.95   $823.95   $823.90