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 $241.69   9.457%   $264.5466   $264.55   $264.55   $264.50  
  Purchase #2 $94.30   12.226%   $105.8291   $105.83   $105.85   $105.80  
  Purchase #3 $61.40   4.283%   $64.0298   $64.03   $64.05   $64.00  
  Purchase #4 $150.83   3.257%   $155.7425   $155.74   $155.75   $155.70  
  Purchase #5 $93.94   11.151%   $104.4152   $104.42   $104.40   $104.40  
  Purchase #6 $226.88   5.396%   $239.1224   $239.12   $239.10   $239.10  
  Purchase #7 $112.55   12.118%   $126.1888   $126.19   $126.20   $126.20  
  7 purchase totals = $981.59       $1,059.8744   $1,059.88   $1,059.90   $1,059.70