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 $219.43   10.332%   $242.1015   $242.10   $242.10   $242.10  
  Purchase #2 $177.87   8.495%   $192.9801   $192.98   $193.00   $193.00  
  Purchase #3 $33.72   4.433%   $35.2148   $35.21   $35.20   $35.20  
  Purchase #4 $102.74   11.794%   $114.8572   $114.86   $114.85   $114.90  
  Purchase #5 $67.31   10.843%   $74.6084   $74.61   $74.60   $74.60  
  Purchase #6 $149.26   6.356%   $158.747   $158.75   $158.75   $158.70  
  Purchase #7 $223.54   8.251%   $241.9843   $241.98   $242.00   $242.00  
  7 purchase totals = $973.87       $1,060.4933   $1,060.49   $1,060.50   $1,060.50