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 $26.44   10.724%   $29.2754   $29.28   $29.30   $29.30  
  Purchase #2 $179.51   13.482%   $203.7115   $203.71   $203.70   $203.70  
  Purchase #3 $48.25   11.838%   $53.9618   $53.96   $53.95   $54.00  
  Purchase #4 $151.57   4.796%   $158.8393   $158.84   $158.85   $158.80  
  Purchase #5 $223.29   7.579%   $240.2131   $240.21   $240.20   $240.20  
  Purchase #6 $225.55   4.378%   $235.4246   $235.42   $235.40   $235.40  
  Purchase #7 $93.38   11.419%   $104.0431   $104.04   $104.05   $104.00  
  7 purchase totals = $947.99       $1,025.4688   $1,025.46   $1,025.45   $1,025.40