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 $62.66   8.532%   $68.0062   $68.01   $68.00   $68.00  
  Purchase #2 $167.30   7.359%   $179.6116   $179.61   $179.60   $179.60  
  Purchase #3 $104.86   10.542%   $115.9143   $115.91   $115.90   $115.90  
  Purchase #4 $74.35   13.334%   $84.2638   $84.26   $84.25   $84.30  
  Purchase #5 $225.56   11.204%   $250.8317   $250.83   $250.85   $250.80  
  Purchase #6 $22.53   9.790%   $24.7357   $24.74   $24.75   $24.70  
  Purchase #7 $195.94   6.266%   $208.2176   $208.22   $208.20   $208.20  
  7 purchase totals = $853.20       $931.5809   $931.58   $931.55   $931.50