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 $82.46   12.278%   $92.5844   $92.58   $92.60   $92.60  
  Purchase #2 $162.56   10.455%   $179.5556   $179.56   $179.55   $179.60  
  Purchase #3 $219.63   7.444%   $235.9793   $235.98   $236.00   $236.00  
  Purchase #4 $104.49   13.393%   $118.4843   $118.48   $118.50   $118.50  
  Purchase #5 $105.35   6.278%   $111.9639   $111.96   $111.95   $112.00  
  Purchase #6 $136.87   12.634%   $154.1622   $154.16   $154.15   $154.20  
  Purchase #7 $235.65   13.168%   $266.6804   $266.68   $266.70   $266.70  
  7 purchase totals = $1,047.01       $1,159.4101   $1,159.40   $1,159.45   $1,159.60