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 $29.58   13.666%   $33.6224   $33.62   $33.60   $33.60  
  Purchase #2 $132.63   11.176%   $147.4527   $147.45   $147.45   $147.50  
  Purchase #3 $240.48   4.770%   $251.9509   $251.95   $251.95   $252.00  
  Purchase #4 $41.49   10.822%   $45.98   $45.98   $46.00   $46.00  
  Purchase #5 $147.57   9.177%   $161.1125   $161.11   $161.10   $161.10  
  Purchase #6 $129.29   9.206%   $141.1924   $141.19   $141.20   $141.20  
  Purchase #7 $223.32   10.155%   $245.9981   $246.00   $246.00   $246.00  
  7 purchase totals = $944.36       $1,027.3090   $1,027.30   $1,027.30   $1,027.40