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 $84.51   4.860%   $88.6172   $88.62   $88.60   $88.60  
  Purchase #2 $165.58   11.453%   $184.5439   $184.54   $184.55   $184.50  
  Purchase #3 $62.75   7.629%   $67.5372   $67.54   $67.55   $67.50  
  Purchase #4 $8.63   6.262%   $9.1704   $9.17   $9.15   $9.20  
  Purchase #5 $74.58   7.276%   $80.0064   $80.01   $80.00   $80.00  
  Purchase #6 $147.47   4.164%   $153.6107   $153.61   $153.60   $153.60  
  Purchase #7 $38.62   11.378%   $43.0142   $43.01   $43.00   $43.00  
  7 purchase totals = $582.14       $626.5000   $626.50   $626.45   $626.40