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 $25.97   13.721%   $29.5333   $29.53   $29.55   $29.50  
  Purchase #2 $168.36   9.496%   $184.3475   $184.35   $184.35   $184.30  
  Purchase #3 $187.56   6.556%   $199.8564   $199.86   $199.85   $199.90  
  Purchase #4 $229.82   3.393%   $237.6178   $237.62   $237.60   $237.60  
  Purchase #5 $41.36   7.229%   $44.3499   $44.35   $44.35   $44.30  
  Purchase #6 $250.29   11.142%   $278.1773   $278.18   $278.20   $278.20  
  Purchase #7 $166.58   4.777%   $174.5375   $174.54   $174.55   $174.50  
  7 purchase totals = $1,069.94       $1,148.4197   $1,148.43   $1,148.45   $1,148.30