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 $201.97   8.726%   $219.5939   $219.59   $219.60   $219.60  
  Purchase #2 $181.85   13.462%   $206.3306   $206.33   $206.35   $206.30  
  Purchase #3 $58.37   7.501%   $62.7483   $62.75   $62.75   $62.70  
  Purchase #4 $56.54   4.379%   $59.0159   $59.02   $59.00   $59.00  
  Purchase #5 $165.91   4.573%   $173.4971   $173.50   $173.50   $173.50  
  Purchase #6 $241.69   7.157%   $258.9878   $258.99   $259.00   $259.00  
  Purchase #7 $147.67   7.297%   $158.4455   $158.45   $158.45   $158.40  
  7 purchase totals = $1,054.00       $1,138.6191   $1,138.63   $1,138.65   $1,138.50