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 $24.67   3.672%   $25.5759   $25.58   $25.60   $25.60  
  Purchase #2 $180.45   3.593%   $186.9336   $186.93   $186.95   $186.90  
  Purchase #3 $22.32   12.591%   $25.1303   $25.13   $25.15   $25.10  
  Purchase #4 $25.26   12.326%   $28.3735   $28.37   $28.35   $28.40  
  Purchase #5 $222.51   12.644%   $250.6442   $250.64   $250.65   $250.60  
  Purchase #6 $74.40   13.761%   $84.6382   $84.64   $84.65   $84.60  
  Purchase #7 $46.68   5.622%   $49.3043   $49.30   $49.30   $49.30  
  7 purchase totals = $596.29       $650.6000   $650.59   $650.65   $650.50