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 $24.73   11.441%   $27.5594   $27.56   $27.55   $27.60  
  Purchase #2 $171.96   5.256%   $180.9982   $181.00   $181.00   $181.00  
  Purchase #3 $238.94   9.767%   $262.2773   $262.28   $262.30   $262.30  
  Purchase #4 $199.86   11.253%   $222.3502   $222.35   $222.35   $222.40  
  Purchase #5 $127.75   12.137%   $143.255   $143.26   $143.25   $143.30  
  Purchase #6 $183.36   11.463%   $204.3786   $204.38   $204.40   $204.40  
  Purchase #7 $123.81   4.788%   $129.738   $129.74   $129.75   $129.70  
  7 purchase totals = $1,070.41       $1,170.5567   $1,170.57   $1,170.60   $1,170.70